Been there--Done That!
I try to gas up every 100-120 miles not because I'm close to running out of fuel but to be able to get off, stretch, walk around etc.
However going across that frigging desert I was stopping every 30-40 miles just for cold water.
Since then I've improved my traveling arraignments and I have a nice soft sided 'Ice Chest' that I put two Blue Ice Packs in along with prechilled bottled water and that works really well!
I've found that most motels have big refrigerators in the office area and will gladly put the Blue Ice in their freezers and more and more (even Motel 6's) have small refrigerators with small freezers in the rooms which works out great!
Ride To Live--Live To Ride!!