Hey man i recommend talking to a shop that builds race cars for recommendations. I help build dirt race cars with tubular frames and huge engines. If done right they are stronger and lighter that a box frame. The only problem is trying to keep the dumb thing straight and level. If you do do it draw it out in every detail. I recommend using a program suchas autocad. By using the computer you can make adjustments and have calculations instantaneously with the computer. Also if you have any engineering buddies have one of them take a look at your design for safety reasons.
Good luck
Nick
Good luck
Nick