I raced a lot of formula Fords, little single seaters and they were all tube frame before monocoque(sheet aluminum formed into boxes for the chassis) or carbon fiber. They were very thin wall square tubing, cro moly 4130 and they were brazed together. Welding that thin metal made it brittle. Brazing is really old school and guys would give us crap about not tig or mig welding but the brazing was really strong and if you had crash damage super easy to go back to the first joint where it was straight and blow it apart with a torch. The chassis also had a little give to it so the vibrations wouldn't cause it to crack. You would need to have a set up plate or a dead level floor which is easy with the new epoxy kits. Then you have a solid level reference for measurements. The sled would probably be ugly but it would tough, light, easy to repair, relatively cheap and exactly what you wanted. Looking at sleds I wonder why the front and rear bumpers aren't tied together through the running boards and why their aren't rub bars on the outside of the side panels.
