[Cory]

We've used 1"x2" 1/8" wall aluminum tubing the last few years, with great success.

Put a couple cross braces in the center, and you're good to go. We got the heck bashed out of us all year long, and the frame is just as square as the day we had it welded. Haven't had a single issue.

I suppose it helped that a professional welder did all the welds on our frame, but as long as you design the frame properly, you shouldn't have a problem.