Don't have a gas motor home but find similar problems with diesel.
I know of only one Wall Mart that we can get our motor home in, Decatur Ind, when they don't put thee piles of fertilizer etc too close to the fuel station. We saved 35.00 last time over the rest of the stations in the area and on up into Michigan.
Costco sells diesel and propane and is set up to fuel a mh but they have strategically placed islands etc so it is not possible for our mh to get to it nor into the fuel lanes where on occasion they have reasonable diesel prices.
Kinda odd since RVers when we do stop there end up spending usually a few hundred dollars in groceries, supplies like tp, water softener, black tank and gray tank aids and assorted things for an RV and gottahaveits.They don't want our business.
We saw diesel for 2.23 in Southern Indiana near Clarksville, but they have now configured the station so only pickups and the like can get in. We had fueled up there many times before.
FJ has two lanes usually but at every one you have to pull close to the building to get in or out of the tight lanes with big bolsters with lots of scars from trying to maneuever. If you get too close at one in Ky you can't open the door to get out to fuel up. If there are cars and especially vans or pickups parked at the building with our toad at 68 ft we have to wait until they come out and leave meanwhile RVs are backed up into the road wanting to get into the pumps.
Some stations /truck stops do have gas at their truck islands but I don't have a list.
Next Exit provides a lot of info on what is at the next exit. Perhaps it list gas at truck islands and so on. I don't know.