About 5 or 6 years ago, I bought one of the $299 4 x 8 utility trailer frames that they used to sell at Tractor Supply. (I just surfed the TSC website and I don't see these utils for sale anymore, but the one I got is similer to this one at HF, except mine is 8 feet long and has 12" tires, and a 2,000 lb axle: http://www.harborfreight.com/870-lb-capacity-40-inch-x-49-inch-heavy-duty-utility-trailer-with-8-inch-wheels-and-tires-42708.html )
At the time I had a bunch of 6" deck planks left over from building (yup, you guessed it) a deck, so I screwed them together and to the trailer frame and ended up with a pretty decent little trash/ lumber/ car parts trailer that I could tow behind any vehicle I owned with a ball.
While it worked pretty well for what it was, there were some things that I didn't like about it. The dutch doors in back sagged when open, and wouldn't stay open if the trailer was parked on a side tilt. The metal fenders that the trailer came with were cheap and brokee off. The lighting, too, was cheap and either broke or was rendered inoperative by water. And the way the tongue protruded out from the front as a single beam, without any triangulation support, didn't seem overly sturdy. Over time, the screws that I used to build the whole thing either backed out or broke, and the door hinges for the dutch doors came off, too.
So, about 3 months ago, I ripped it all off down to the bare metal frame and started over. I worked on it occassionally, mostly a few hours at a time at night, maybe once or twice per week (interspersed between other projects), with a final "push" these last 2 weeks, working every night and both weekends. And now...
All of the wood on the trailer is framed in with 1/8" thick metal- 2"x2" angle iron front and back, and 1-1/4" angle iron around the fenders. The fenders are now inset into the carrying box, so the full track is now the interior width of the box. This looks a lot better and increases total volume by over 25%. The rail on top of the right and left sides is 1-1/4" 'C' channel, which fits over the plywood sides snugly. All the plywood is pressure treated 3/4". The bottom is two sheets thick, for extra strength.
The back now has a tailgate, with hinges at the bottom made from 3/4" round bar inside of 7/8" ID tube. It's cross-drilled with hitch pins so the bars can be removed and the tailgate can come off. Also, the stop/turn/tail combos on the tailgate ($14 each, 13 LED strips) are wired into the trailer with a flat-four plug, so they can be unplugged when the tailgate is removed. Of course, this makes it non-street legal, but I don't anticipate running without the tailgate on the road.
The tailgate wiring is protected by that aluminum strip that runs most of the width of the gate. I cut a groove in the tailgate plywood for the wiring to run in. I also cut out aluminum panels to close off the wheel wells inside. Those were the last things to install, last night. There's two latches on the tailgate, one on each side, $8 each from tractor supply, lockable, that latch onto the 2" angle iron on either side. All plywood is reinforced with metal, and bolted, not screwed.
The marker lights are LED, and armored. I think they were like $8 each. I rewired and regrounded everything, and the lights are super bright. Another benefit to widening the cargo body was pushing the marker lights out further, which makes the trailer easier to see behind my pickup.
I added a folding, wheeled tongue jack ($49) which makes rolling the trailer around the yard a breeze. The height of the cargo box side is 2', which I calculated to ensure the top of the box was at or below the bottom of the rear window of the lowest potential tow vehicle. I also made sure there was at least 96 inches between the inside of the front and inside of the tailgate, so 8' long hard goods can be carried gate-up.
A couple of things I plan to do in the future...will probably replace some of the bolts with eye bolts to provide hard points for securing loads. This will be very easy. Also, as it turns out the bolt pattern of the 12" trailer wheels is 5 x 4-1/2, so I might stick a set of 15" volvo 122 wheels/tires under it, with 122 hubcaps. This will be a nice little touch for when I'm towing it with my Amazon wagon. ;-) I made the fender opening large enough to accomodate those wheels, too. I'm also contemplating some sort of folding canvas cover, to create a completely covered box big enough to stoop in. For now I'll probably just tarp it with bungees/ ratchet straps as I have before. There's no provision for a license plate, as SC does not require them for small trailers like this, but it could be added to the tail gate easily, along with a light. I may add a vertical piece of steel above the corners of the wheel well to better tie into the C channel, though it's pretty sturdy as it is.
I didn't keep a strict budget when doing this, but I'd estimate that I have around 5 sheets of 4x8 3/4" plywood, a few hundred screws, about a hundred bolts/nuts/washers, and a few cans of rustoleum into the project. Some of the steel was reclaimed from a junker trailer, but I did buy about $150 worth of additional metal/aluminum. The lighting and jack were another hundred or so. So, maybe around $400, on top of the original trailer price of $300.
