I once took a BN2A islander to Malaysia. We made a wooden cradle for four 45 gallon oil drums. We specified the type that has both a screw on top at the end of the drum and one in the middle on the side of the drum but opposite the cap on the end, if you know what I mean.
The cradle was made from wood and secured to the floor, the drums were strapped to the cradle. The fuel pick-off was via the cap on the end of each drum, suitably modified with an appropriate fitting. This cap was obviously positioned at the bottom so the fuel would flow. The barrels being laid on thier sides in the cradle. Thus the cap on the side of the drum was now at the top and was used to fill the drum. Get the picture?
Each drum had a bendix reciprocating fuel pump secured to the cradle and was plumbed into the crossfeed line of the main wing tanks. The operating switches were secured at the pilots end of the whole rig, just behind the pilots seat. Obviously a suitable C/B protected power supply was conncted.
As the aircraft was British registered the whole contraption had to be approved by the CAA as a modification, and the local surveyor came down to inspect the device.
It was approved and off we went.
I don't know what you have in mind but you might find that there is already something out there for your aircraft, already approved. Talk to your local authority, they might be able to help.