I have seen fuel (gasoline or diesel) carried in 2-3 different places outside a class "C":
1: With a Jeep Wrangler toad soft-top, the fuel canisters were both places in the toad, and a few were bolted to the back, allowing for 20-30 additional gallons.
2: A rack was placed on the roof, with the cans attached to that.
3: A new bumper was welded on (the factory bumpers will shear off very easily), and the fuel cans mounted on that.
4: A rear hitch mounted cargo rack was used.
Of all of those, if one hasn't done it already, I'd go with the hitch mounted cargo rack.
