Tonneau construction material question

I'd like to build a rigid tonneau to cover the passenger side of my Miata. Something that rests on the dash top and a bar between the shoulder belt mounts. I could make it out of a sheet of plywood, but that's heavier than I'd like. What else is readily available that would be reasonably rigid , but lighter? I'd cover whatever I build with some black vinyl from the fabric store. Ideas?

Fiberglass

Coroplast (much quicker probably, but maybe not quite stiff enough). You could use two layers glued together though, I bet that would be stiffer.

You can get coroplast in 10mm thick in addition to the standard 4mm. The 10mm is surprisingly robust and will work great. If you want overkill you can also get aluminum skinned 10mm Coroplast that you can damn near stand on. Be aware though, glue and paint have a very hard time sticking to coro. Your local sign shop should be able to get any of these for you. In fact, if you want it a specific color, I'd talk to them about covering it in solid color lettering vinyl after you finish it. Should be pretty cheap to "float" it all one color.

All I know is if you drill holes into the dash to secure the cover, don't put stress on the fasteners. My 1991 had a cracked dash because of that.

Fiberglass, sheet aluminum with clever stiffening ribs.

I don't want to work with fiberglass at this time of year, but the 10 mm coroplast sounds like a decent idea. I was looking at how to anchor something to the dash but I'm in agreement with RossD on that. I'm envisioning something rigid that I can bungee to the seat belt buckle and the bar behind the headrests.

A sheet of aluminum sounds like a great way to slice yourself in half in a side impact...

I'm assuming you'd have a vertical flange along the edge, because that would be the smart and lightweight way to add a bunch of rigidity. It would also cut down on the sliceability.

I'll be interested to see how the coroplast works. Seems to me it would only want to curve on one axis, which may make fitment a challenge.

In similar news, here's a car we're delivering to a customer this week.

Fiberglass, obviously. It's attached with three studs and grommets along the passenger "door" (motorcycle fairing hardware) and a quarter turn fastener front and rear on the driver's side. Solid, easy to remove. But check out those compound curves.

Warren, what are you actually looking to accomplish? Seems to me the actual Mazda tonneau would be the easiest thing to live with. Heck, I know it is, I ran one for years. It could be deployed and stowed in seconds.

There was a factory Mazda tonneau that covered the passenger seat?

I want to block off the passenger side to stay warmer while I drive top down through a significant part of the winter. That's just for gits and shiggles. I'd love a proper tonneau, but they're $300-600 and the car is 16 years old. Not worth the expense.I'm looking for any way to easily, and cheaply create a tonneau that looks reasonable, not necessarily professional. I even considered sewing up my own. One detail that matters is I have a homemade windblocker right behind the seats and to drive the car below freezing I'll want to keep it.

thatsnowinnebago wrote: There was a factory Mazda tonneau that covered the passenger seat?

There sure was. Had a Miata logo embossed behind the seats, too. The factory one was smooth, you had to scoot the seat forward and lean it all the way back to fit underneath. The aftermarket ones all have seat pockets which would be more convenient but look clunkier.

Keep your eyes out for a used one, Warren, I bought mine years ago for $100. The age of the car isn't really a factor if you're driving it. I can tell you that the windblocker is going to be a LOT more effective at keeping you warm in inappropriate temperatures. BTDT with both variations.

doc_speeder wrote: A sheet of aluminum sounds like a great way to slice yourself in half in a side impact...

That's exactly what I was thinking. Fiberglass too.

You need to look for solutions instead of problems. Put a vertical flange along the edge and you get rid of the thin edge AND gain rigidity at the same time.

Mock up from cardboard and have an awning shop match the shape, weld up and stretch fabric around an aluminum frame. Or go GRM and do that yourself.