[Not2B]

If you can't weld Al (skill-intensive), and you don't want to use 80-20 (expensive)...

Rivits! Pop rivets are good when used correctly. I love pop rivets. You can be pop riveting after a $16 investment at your local hardware store.

And for wood - that is nature's composite. Most lumber only has the fibers (that resist tension) running in one direction. That's seen in the grain. But you can get plywood with the sheets running 90 degrees from each other. When used correctly, in the correct applications, wood is good.

Basically - there is no correct answer - each application, each material, and each design need to be considered and evaluated based on what's important to you. That's engineering...


Edit:
Oh yeah, on the kit frame - if you worry about it's rigidity, take a sheet of plywood and put it inside the C-channels to give it a solid wood floor. Bolt that sucker down, and the frame is going nowhere fast. (But the kit frame is DARN nice... and more modifiable than it's given credit.)