trex frame questions

i know you guys have seen them the trex's wheels one in the back and it seats two well im wanting to build one my self and was wondering if anyone had any info on them as far as the frame goes. Like the over diameter of the round tubing it looks like 1 1/2 but i dont know what a safe thickness would be for it. I would appreciate any info ou guys got on it.

picture if you havent seen it.

http://www.trexvehicles.com/pictdealer/21.jpg

o T rex i thought you were talkin about the fake wood shit they make patios and decks out of im not sure what they use but its not a very heavy vehicle 3/16 thickness is more than enough

yea i was thinking about that size too would be great just dont want it to heavy because of speed. But thanks for the input any body else