I carry a 250 L tank from a Freightliner:angel: on the draw bar of the camper I built. It's inside a box made of dexion frame covered with marine ply. The framework has no structural significance for supporting the tank
https://www.aulro.com/afvb/images/im...012/02/807.jpg
The tank is held in place with the original "strapping" as fitted to the prime mover with the cast fixtures bolted to two cross pieces welded into place and strengthened with gussets.
The tank was 6 months old when I bought it with all fittings and fixtures for a shade under $500. It's light enough to easily manhandle into position when empty... Came with the sender so I simply bought a 12V fuel gauge from a boat supplies. The calibrated gauge takes its power from a distribution board inside the camper housing 2 x 105 AH super charge "All Rounder" batteries hooked up in parallel
https://www.aulro.com/afvb/images/im...012/02/808.jpg
I fitted a Schraeder valve and pump in 4psi max with an ARB compressor. I then open a ball cock and ULP flows into the main tank through 4m of 10mm (ID) fuel hose. Takes about 15 mins to dump 70L. Depending on the external temp, I sometimes need to top up the pressure with a couple of seconds burst from the compressor. I never exceed 180L petrol in the tank when filling it. works well!
EDIT: Towing that lot to the Cape and back plus some touring... over 8,000km or thereabouts...overall consumption was a shade under 18L/100km. At a steady 90-95 on the highway it dropped to 14.5L/100km

