When generators are run off motor home fuel tanks, there typically is a dedicated supply line in the fuel tank that sits higher than the one for the engine. This prevents you for running the tank to empty with the generator and then not being able to start the motor home.
I think it would be easier to have an auxiliary tank in the spare tire location that feeds the generator and truck while the main tank would remain dedicated for the truck. Marine style quick connect fuel fittings could be used between the truck and generator, but you may need an additional fuel pump if the rise or run of the fuel line is too long.
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