The first one I built i managed to pick up a sloping custom tank at the old sod, fitted behind the rear seat after removing 20" from the rear
a mini tank fits in the rear over the arch quite nicely, one each side if you can get an off side mini tank (rare) and you can route through the c panel....
a mini van / traveller tank is ideal as its long and low...
more bobtail info on the site...
http://bobtail.org.ukCheers Steve