What exactly are you wanting? You can purchase steel or aluminum tubs for cheap, but they only make a couple radii, 36" and 40" I believe, and there is a ton of time used to make them fit.
Most race car guys cinsider mini tubs to be where you cut out the factory tubs and put the above mentioned tubs in. You're limited to the factory frame rail location for width.
Another way to do it is to remove the inner wheel well and move it over closer to the frame, you then just add a strip of metal in the indented area of the halves and you'll have to modify where the trunk hinge welds to the inner tub.