I full time. When I decide that I am going to stay in one place for a week or so I do not top off the tank before hand. I also don't run with a full tank ever.
My gas tank, water tank and gray/black tanks are all behind the rear axle. So depending on how much water I am carrying dictates how much fuel I will carry at the same time.
Other tanks all empty then the fuel tank gets more and I will top off while traveling because it affects my handling if too low.
Makes a difference HOW you RV. Distance, duration etc.
I DID find out just where those pesky vents are though. When they fell out I knew 'exactly' how much fuel I could put in before it poured out all over the gas station. :W