I'm now planning on getting the AEV bumper/carrier/aux tank.... trying to work out a decent way to transfer fuel to the main tank.
I'm thinking of drilling a hole in the top, and fitting a pickup tube... Using something like this: 
Bulkhead-Fitting-Aluminum combined with a small pump that can be triggered via an AUX switch to transfer fuel into the main tank.
but.... I'm concerned about the possibility of pressure in the aux tank pushing fuel into the main tank either overflowing the main tank, or emptying the aux tank over time without realizing it, only to find it empty when I need it.
Any thoughts on a pump that would block the flow when it's not on? Seems like that's the most straightforward solution... or adding an electric valve that opens when the pump runs. Or plan "C"?