The steel 55 will fit in the spare tire well of a bunny.. It's a tight fit, I had to bounce it in there with a mallet.. Nice part about that, no hold down needed... IIRC I did massage things a bit at the very bottom of the well so that it would fit down down against the bottom, otherwise there was a half inch gap.. I could have made it shorter, but that ran into fitment problems for the goodies in the tank.. I welded a 2" wide ring (like a donut) to the top where I had cut it off, then made a round plate that bolted to that with a gasket so that I could open it up if need be.. The fuel gauge sender (universal type), pickup and return, and a nipple for the filler are mounted in the "lid" as was (for my case) a heat exchanger.. The pickup was just 3/8" brake line welded in there with no screen.. I opted for an inline fuel filter outside of the tank for easier cleaning..I think when I was all said and done it turned out to be about an 8 gallon tank.. I'd imagine less the heat exchangers it would have been about 8.5 gallon.. A solid lit would work fine for plain ole diesel, since I used it for WVO I wanted the option to be able to get in there and really clean the thing out if need be.. Kevin, baffles are a MUST!!! I did not put baffles in my tank, and I have darn near paid for it several times taking a turn a bit fast on wet roads.. So far the guard rail and poles have gotten out of my way...
My Caddy came with a 30 gal belly tank, and needed air springs if it was full.