We nver exchange because we have side-mount tanks. We drive up to the fill site, park, go in and get the guy and when he comes out, we remove the tanks (can't fill horizontal tanks, gotta be upright to fill) and we pay him.
For those that don't know, many Ace Hardware fills tanks and nearly every U-haul yard does too. both charge for the gas by weight, not by "tank fill"... So, you get service, keep your tank, and pay at the meter for what you get - both Ace and U-Haul have that policy in most stores. I've seen a few Ace that exchange, but all U-Haul seem to have onsite fill tanks.
