If you want an opinion about the tub, I agree with getting an aluminum one. It's easy to say you don't have the money, but building up a tub from scratch, with all the associated jigs to keep it square, is just not cost effective for a one-off application (Unless you're planning a super-simple comp-buggy that's doing away with nearly all of the body anyways). You'll be two to five times the price of an aluminum tub (including your labour, welding equipment, fabricating equipment, replacement body panels, etc). The canadacruiser.com panels run around us$1200, and they don't include the front floor/seat area, or the B-pillar, or the inner & outer lower door sill. You can get most of these parts from CCOT, but they are big $$$.
Again, this is just my opinion. I just wanted to try and share a little experience so you don't end up going down the same LONG road that I did.
Cheers,
Steve