[TRUCKMAKER]

I have to agree with Nathan. If your making truck frame rails buy the rails available from Ric, it will save you a lot of time and headaches depending on what kind of tools you have. That being said, yes you can get the u channels at most well know hardware stores. The rails that work with Tamiya are metric and the channels at the hardware store are SAE. They are slightly taller than "tamiya" rails which means any frame brackets or fuel tank brackets that mount to the top and bottom of the rail must be modified to fit which is tedious and makes the mounts quite thin. The web portion of the U channel which is actually known as plywood cap is about a 1/4" too wide and must be cut back. You'll need a good industrial grade metal cutting bandsaw or a mill with a table and vise long enough for the length of rail your making. If you want a prototypical look you'll then want to grind or sand the square out board edges round. Then you might be ready to lay them out and start drilling and tapping holes.
I'm one of those few guys that have done this, its not worth the few bucks you'll save. I did it because the rail supplier at the time was out of product and the current supplier, Ric at PMD, I don't believe carried the rails then. It can be done, look up "Knight Krawler" and you'll see a set of rails made from plywood cap. If you like doing everthing I just said, have fun! Happy building, Kent