Armalite

I am trying to mount an older ford gas tank in the spare tire location under the truck. The plan is to get an 18 or so gallon tank and use the factory ford fuel pump to fill my stock tank. The range between fill ups is depressing. I have looked into Jerry cans and transfer tanks that sit in the bed but I want a system that works by flipping a switch and not having to stop to fill up.

I think I need some kind of one way valve that would be able to hold a vacuum so the factory evap system could still function. Ideas?

If I fill the factory tank would the pressure be relieved through the factory evap setup? Rigging some kind of auto off switch to prevent over filling would be nice. I haven't looked into the auto off switch much yet.

I haven't seen this done much and aftermarket options aren't around or affordable. Let me know what you think and if you know of any build threads please link them.