Always keep it more than half full?
Hahaha. Seriously though, you might want to see at what point it starts to just suck gasoline, and no air. You might want to drop the tank, or unhook it, and check the lines to see if they, or the glass bowl on the fuel pump it leaking.
Th bowl on my fuel pump seeped a tiny amount of air, and the truck wouldn't start right at all. I had a rough surface on the pump, from my old nemesis, corrosion.
