Loading or unloading a dolly under adverse circumstances can be a PITA, but that's not why I'm replying to this thread. I'm replying to address the issue of fueling while dragging the tow dolly & vehicle around... my suggestion would be to fuel at larger truck stops or "travel plazas" (as they call 'em now, since they also cater to the RV crowd, four-wheelers, et al). The lots are generally larger to accommodate trucks, and there are separate fuel islands for four-wheelers & RVs, though a diesel RV can always go through the truck islands to refuel, UNLESS you see a sign to the contrary. Those truck stops or travel plazas want your money, so usually it's no big deal.
When I drove my 26' rental truck with tow dolly & four-wheeler behind, I almost always used truck stops or travel plazas to refuel, unless I had no choice. They're larger, they're usually better lit, the big ones have security, there's more stuff to buy in the store (including spare parts and bulbs and whatnot), more food choices in store & restaurant, more urinals and stalls in the bathrooms, the whole nine yards. Why frequent small service stations with limited room to maneuver? I don't see the sense in it... the larger truck stops or travel plazas have the room and can't be beat when it comes to fuel prices, they're big enough to lowball the competition. Meh, why make things harder and pay more?
Yeah, there are some older truck stops that are tight in the maneuvering sense, generally back East, but the new modern travel plazas are nice, and they start by building on huge lots, compared to small service stations. Even the separate fuel islands for four-wheelers & RVs generally have more room, which is nice when you're swinging wide because you're pulling a dolly & vehicle behind you. I've seen some service stations so tight that getting a single four-wheeler in & out of there was difficult, I certainly wouldn't wanna get stuck in some hole like that and have to go to a bunch of trouble to extricate myself and my rig. Just my $.02 on this subject... KISS principle works for me, lol. Cheers!!!