Auxiliary gas tank question

I have a RDS 80 gal tank in mine. I plumbed the roller over check valve into the vent line in the filler neck. The tank is gravity fed through a manual ball valve right at the tank then a 12v solenoid valve under the bed into the filler neck. I have no atmospheric openings, fumes have to go into the main tank. The aux tank is always at the same pressure as the main tank.

I've forgot to shut it off a few times. The truck will miss and die for a bit, doesn't like being overfilled. Gas can also run out the vent line. You can't leave the valve open for this reason and the computer likes to see the fuel level drop to keep accurate track of usage. I usually wait until it's half then turn the aux tank on.