A lot of aftermarket commercial bodied trucks have a similar issue. I had a 1987 F350 dump truck that I would lift the bed in order to fill the tanks... otherwise I had to "trickle fill" it and listen for the sound of the tank filling up, and check the fuel gauge to see if it was all the way full.
This is usually due to the path that the fuel filler tube took due to the custom body. At fuel pumps, you may notice contractors carefully filling their custom bodied work trucks, it is annoyingly common.
With my F350 it had nothing to do with the fuel pump or fuel nozzle.
You might be able change the location or rebuild the fuel fill tube on your camper.
Otherwise you may be stuck just trying to fill carefully.
