Gday Aaron,
I did the canning trip with Roger (Disco WA) and I had a 59ltr plastic tank from a camper trailer sitting on the floor behind the front seat,then got some plastic hose and a hand pump and mounted the pump on the cargo barrier..worked a treat, was abit of a hassle to fill as I had to do it in the car..but was no major problem.
Cost,59ltr plastic tank=$139
Handpump that suits camper trailer=$19
Plastic hose in 2 sizes 1 filler.1 to pump=$12

and it is now fitted as an extra tank on my camper trailer..

Cheers Ean