I once drove from central Alaska to New Mexico (near the Mexican border) in about 4, 16 hour days, roughly 4000 miles. Gas-n-go until crashing in a hotel. I'm still sane.
One point for the original poster, I have a 36 gallon tank in my truck. I rarely let it go empty because it's annoying to have to use the credit card twice at the pump. Every gasoline pump I've gone to has a limit, usually $100, then the pump turns off.