I did the same thing you plan to do. I actually had this tank fabbed by a company in Texas under $250.00. PM me if you need details. Anyhoo... I had the tank made to actually go back under the seat. But, once installed it still gave me the chills. So, I checked out the under bed area and wah-lah, it fit perfect. I countersunk a marine fill neck into on the bed planks and away we go. A new factory style sender float had to be modified (shortened and bent a tad) to work but it all works perfect. I fabbed the straps, etc. It holds about 12 gallons I believe.
Under Bed Tank '46