Clamping a 2x4 to the bed rails of a 3rd gen

I do not know your experience with wood, but ...

2x4s warp badly with exposure to moisture. They bend, they cup, they twist. In house construction skilled carpenters can line up even cupped 2x4s can be used, but that is inside the walls with great skill and judgement. Just go to Lowes and look through the pile of 2x4s to see what I mean.

Plywood also warps if the edges are not secured to something.

2x4s are notoriously rough edges (not millimeter-tolerance flat), need anchoring at many points to avoid warping. Wood furniture in a humidity-controlled house is one thing. Wood exposed to extremes of cold/hold/dry/wet can be a nightmare.

 

I have built houses and airplanes (full size that carry people) and various other things out of wood. For the airplanes the wood is varnished to help seal it against moisture but it isn't sitting in water. And it depends on the quality of wood. You don't built airplanes out of big box store wood. It's hard to find lumber there good enough to build a shed sometimes. If you use crap for wood and don't protect it from water you are going to have problems. But there are ways to make it workable.

 

Taking off the plastic on top of the bed rails and adding a couple bulb seals is how AT mounted my AT Habitat. The flat surface, I've read, is easier to seal (even with the holes). Some type of tape can be laid down flat over it all, then the bulb seals added. Next, I'd suggest thinking about using plywood in place of your Clamp. Screw a strip of plywood (4-6 inches?) to your 2x4, hanging down over the Tacoma's bed track. You can get large square nuts to slide into the track, and then bolt through your plywood into the bed track.

AT used aluminum angle iron, but the 2x4 and plywood would take it's place so you can stick with wood construction. Drilling the holes perfectly to line up could be a challenge, but if you are taking this project on I'm sure you can handle it. I'd also refrain from drilling those holes until your camper is finished, with as much weight as possibly compressing your bulb seals, as you obviously won't have a screw/clamp to compress.

 

Easy to deal with the hole locations. Put the plywood on the bolts before screwing to the 2 x 4. Build up the whole cover so the seals are compressed. Then screw the plywood to the 2x4s.

 

See, this is why I leave the carpentry to the professionals

 

I wouldn’t use plywood for the connectors unless you want to see the traffic pile up the wreckage of your cap causes in your rear view mirror. Plywood just isn’t strong enough to use in this application. Only use clamps if you provide a lip for them to engage and are fastidious about checking them. A metal strap to the bed rails with bolts and lock nuts is best and you still want to check them.

 

You are really being dramatic. Plywood could be fine for this - depending on thickness, number of fasteners, etc.

 

Or go with material that does not swell/shrink due to heat/cold/water, that can be "cast" as smoother than the surface of a 2x4.

"You get what you pay for".

 

For the shell, yes. But I would still use steel for the straps that connect it to the bed.