Be darned if I can remember what it come out of but there are tanks that will fit between the frame and drive shaft. Built a 46 around 25 years ago and it has a junk yard tank in it. Had to make mounting brackets and move filler but was not a hard job. Filler on drivers side and holds 16-18 gallons IIRC.

http://s32.photobucket.com/user/coilover/media/Trigger%20005.jpg.html


Evan