Experiences with different approaches to frame/large part rust protection

So later this week I'll be sending the DMC's frame off to be media blasted to remove the old (and at this point pretty much useless) epoxy coating intended to protect the steel frame from rust. It will be a little while before I'll be needing to re-coat the frame to (hopefully, at least for another few decades) keep it from rusting so badly again, but since the place that is doing the blasting also gave me a surprisingly reasonable quote for powder coating it down the line I have been thinking about whether or not I think that's the route I want to go or not. 

So far there are three approaches that I can think of for handling re-rust protecting the frame:

1. Powder Coating
2. Galvanizing (either via hot dip or electroplating)
3. DIY (using something like POR-15 or the likes)

I have a bit of experience with powder coating since I had some of the suspension parts powder coated when I did the original work on the DMC, and the quote that the place that will likely be cleaning the frame quoted about $300 to powder coat the frame. My concern with this though is that the parts that I had powder coated like 12 years ago really don't still have the powder coating on them. 

Galvanizing (zinc coating) the frame seems like it would be the most 'production-like' approach, but a) I don't know what it is going to cost, and b) I've seen concerns posted regarding how some older car frames (like the DMC) would handle the hot dip. Electroplating sounds a bit less problematic, but again- I don't know what the cost would be or whether there are any places nearby that can handle something as large as a car frame.

Finally, doing it myself using something like POR-15 or another brush/spray-on coating. Ironically, this would probably be more expensive than the powder coating despite the only cost being the material itself (it looks like a gallon of the stuff- of which I'd assume I'd need several- is over $200).

I'm guessing that others here have more experience with trying to rust-protect entire frames and will be able to weigh in with their experiences! 

On the DeLorean, probably closer to a quart to POR-15 the whole frame, maybe two at worst.  If you go POR-15 or powder coating, you'll probably still want to shoot some rust preventative in the frame cavities.  Eastwood sells some, but I suspect you might get it at a better price elsewhere.

I wouldn't use POR as it's made to go on rust does have a history of peeling off. Possibly due to bad prep but I've seen it enough that I wouldn't trust it.

My thought would be electroplating if that is an option, second would be just prime and paint and give it a heavy coat of fluid film/surface shield/ waxoyl that is refreshed as needed.

This is the first I've heard of powder coating not lasting.  The Hard Dog roll bar in my MIata is powder coated, I've had it over 20 years and it's not coming off.  Perhaps there are different types of powder?

Of the three listed (and without doing any real research into it), that's the one that sounds best to me.  My impression is that the POR-15/painting stuff is really intended for when it's too expensive/too much work to get the parts stripped all the way down, but it sounds like you're already doing that.

There's a place in the UK called Retropower that builds high end restomod type cars.  They use a zinc spray process on all their projects on the undercarriage and inside body panels that looks interesting - they'll sandblast, then immediately do the zinc spray, followed by epoxy coat. I don't know if anyone in the US does anything similar.  They have a YouTube channel, and show the process in some of their videos.

I've done this two ways.  For the first (in the early 90s), I sand blasted the frame, blew it clean (that took a while), and coated the insides with rust converter.  With the frame suspended from a chain hoist, the lower holes were taped shut , rust converter poured in various places, and the frame tipped in all directions until the converter stopped running out.  Then the frame was painted with self-etching primer and Emron.  Quite a messy process, but that car is still on the road.

For the second, I had the frame powder coated a few years ago.  The jury is still out on how well that will last, but the process was easier and took fewer years off my life.  In my experience, powder coat done right holds up well unless it is crushed or broken, like where bolts go through suspension parts. Washers help prevent that.

So I had asked about something related (how to deal with replacing the integrated captive nuts that I'd had to cut the bolts off on because the nuts were just spinning) on the DMC forum, and someone had sent me an excerpt from an article from one of the DMC experts in Europe who talked about not using zinc dipping on DMC frames because of their being fairly thin sheet metal and having to do extensive reworks on the frames they'd tried hot dipping to get everything back to the proper dimensional tolerances it needed to be at.

At the moment I'm pretty heavily leaning toward the powder coating option as it seems like for my purposes it will be 'good enough' and be the most cost-and-time-effective. The DMC isn't going to be driven in the winter except under extremely unlikely circumstances (all of our other vehicles would have to be unusable and there be no other way to get where we needed to go), will be kept in the garage (or at a minimum under the canopy in the driveway), and since it's going to be getting a plug-in-electric drivetrain it's likely not going to have a huge range anyway. 

Now I just need to hear back from the people/places that have mobile blasting setups with what they'd charge to clean the frame to see whether I want to go with that or just taking it to the place that will be doing the powder coating.

Powdercoating comes in many flavors.  The most common is Polyester, followed by Polyurethane.  Then there is Epoxy which is not very UV resistant, but tough as nails.  After that you have ceramics and hybrids, but they are specialty coatings.  Powdercoat is basically powdered plastic that you spray on and melt with heat.  It's a little more than that since there is some outgassing and curing reactions.  It's like saying that paint "dries."  It does, but there is more to it than just melting plastic.

Powdercoating is much more durable than most paints, so it will hold up a bit better to being peppered with small road debris, but trust me, it is by no means indestructible.  If you scrape it on something, it will peel off just like paint.  The downside then is that you can't really touch it up.  It's nearly impossible to get paint to stick to the powdercoat.

The other downside is that powdercoating won't go in all the cavities of the frame, so it will just rust from the inside out.

I'm also curious about the quote you got.  $300 won't even get most powdercoaters out of bed.  The reason I got into amateur powdercoating is because in many areas, it's blisteringly expensive.  I was quoted $1200 to do a roof rack that I did all the prep work.  Not to mention, the coater is paying a hefty loan payment on an oven that is big enough to fit a whole frame, and with commercial electric rates and the fact that the oven is probably consuming about 50kW, that works out to be about $20-40 just to turn on the oven.  If that's the real price, and they guarantee their work, that's amazing.  Just know that you're probably getting what you pay for.

I won't speak intelligently about galvanized plating, but I would assume the same reality there... prep.  You likely can't galvanize rust, and anywhere that hasn't had the oils baked out of the pores won't be galvanized.  I also assume the same about hot dip.  You'll also plug every threaded hole with zinc if you hot dip.  I looked into anodizing some aluminum parts.  I couldn't find anyone who would touch them because they can't know the history.  Has it ever been scrubbed with steel wool?  Has it been in an oily environment?  The results of plating work rely heavily on too many factors for most shops to take on the liability of the outcome.

That kinds seems like hot dip is the wisest choice, but I'm not sure if I would like chasing 200 thread holes.

I'm looking at doing a frame soon on an old Pontiac.  When I get to that point, I'll buy a steam genny for my pressure washer and start there.  I will go with a POR or something comparable.  The way I see it, the factory made that frame in 1966, put a light coat of lacquer on it, and it has survived pretty much unscathed for almost 60 years.  I think stripping and painting it will preserve it until long after I'm dead.

I would use POR after stripping the frame. Do all the hollow shapes have openings that can be used to soak the inside somehow?

I wouldn't expect powder to hold up to road wear - putting you back to square one. 

I sandblasted every square inch of my '61 Chevy Apache, except under the roof skin because I didn't want to cut it open.  Everywhere else I sprayed two coats of epoxy primer (and commercial fleet paint), including finding a way to spray deep inside cavities, all in the effort to 'slow down" the rust process.  In theory, it could last another 63 years, at which point I will be well over 100 and probably shouldn't be driving it.

Epoxy Primer and good paint will go a long way, and best of all - easy to repair or touch up when it's scratched, damage, or you need to make welded changes.

I debated Powder Coating, but I am not seeing it as durable or versatile as I'd like it to be.  I have had a few powder coated items brought to me to repair, only to find the powdercoating is stuck to the ghost of what once was metal behind it.

Epoxy primer today is DANG good.

I did POR on the Rover frame. It had been blasted and I prepped it with Metal Etch - basically phosphoric acid. Spray on, let sit, rinse off and watch your lawn turn green :) Absolutely no adhesion problems after 20 years - even on the rock sliders that have seen serious abrasion. They've scratched, but not peeled. 
 

I also did the frame of my Locost the same way. It was brushed both times, it self-levels well.

I think it took a couple of pints to do a frame. Definitely not a gallon. 

The reason I like POR is that it's patchable. Need to add a bracket or something? No problem. Grind it clean, weld, repaint with a brush. With powder, you're unable to change or fix anything once it's done. 

IIRC Exomotive charges something like $900 for a powdercoat job on a frame, and it's a good deal. 

how do you get inside the box sections to clean out  or neutralize the flaky rust  inside ?

and since it is rusting from the inside out ,  how can you figure out how much metal is left until it rusts thru ?

when we have sandblasted what we thought was a pretty solid car its amazing how many holes you end up with where the metal  was  very thin from rusting from the inside.....