Gregg - I looked through your photos, and I did notice the rust in the floorpan. Like you said, it's not nearly as severe as in my truck, but yours suffers from the same condition as most Rapages, Shelby Chargers, Omnis, etc.
Your cage looks very, very impressive. I was a little surprised to see that the floorpan rust hadn't been addressed before the cage was fully welded in. My intention is to fix the rusty bits first, then start on the cage.
Do you know which class(es) you intend to run, Gregg? The cage looks like it is suitable for any speed that you might expect to achieve.
Stainless - good point about either sealing or leaving drain holes. I agree that sealing will be the best course of action. I work with carbon steel all day long, and there are some decent ways to prevent corrosion in the products we make. Of course, our products don't typically come in direct contact with high amounts of salt and water. I'm thinking about applying some anti-rust coating and possibly "emitters" inside the tubes before they are completely sealed.
Steve.