Aux fuel tank plumbing?

[Jarod]

Howdy everyone.
I'm in the process of adding an aux fuel tank, for range purposes, I have a 19 gallon tank that fits nicely in the trunk against the existing fuel tank wall.

I thought about bringing a hose out and teeing into the fuel supply line, but then realized when the tank arrived that the fittings were all on the top. so gravity feeding isn't going to be an option.

I have also thought about a small pump and some wires to a switch so I could watch and when my main tank starts getting low, switch the pump on and transfer diesel into the main tank.

Or I could add some form of solenoid valve to allow me to select tanks like people do for alt fuels.

My goal is added range, extra diesel capacity, and it will likely be temporary, as I rarely need 40 gallons of fuel at my disposal, however it would be handy for some long road trips I have planned.

Any thoughts or advice on the simplest, most foolproof plumbing solution to allow me to go as far as possible without stopping for fuel?