Brad,
Thanks for that great explanation, with some pictures from Ron, I know exactly what you are desscribing. That kind of fab wouldn't be too hard to do. I have also thought about simply buying some stainless steel sheet and cutting my own custom tank if I could not make something off-the-shelf work.
Brett: I have worked with a truck before that had the tire mounted in the bed and it seemed to always be in the space I needed so it ended up just "floating" around lose in the bed. This of course wouldn't be a problem for a non-hauling type of truck
