My Roadtrek 210P on a Chevy chassis had the same problem. I found that it was variable pump to pump and (as others have suggested) the slower the gas was pumped the better the results and that adjusting the angle the pump was inserted had a big effect as well. Many times over the years I just barely squeezed the pump trigger and took quite a while to fill the tank. I never put the pump on trigger lock (even at the lowest setting in the handle) and just gently squeezed the gas into the tank.
I suspect that with different emission control laws and subsequent filling nozzles in various parts of the country, you may well find this is less a problem in some places than others. With Roadtrek, it was a known problem and had to do with the modification (Class C) from the original Chevy design of the the fill pipe to the tank.
Paul