Where do you fuel? If I use the large nozzle/high speed pumps for 18 wheelers, it does not work well unless I just dribble it in at the lowest speed I can manage. Using a standard nozzle and speed (like at Flying J's RV island) works fine.
I don't agree with a vacuum being normal - I think I would look at the cap to see if it is the vented type or check to see if the system has a oneway valve that will vent the tank as the fuel is used but not let the fule escape except when excess pressure builds up and it vent the tank.
I have seen the tank supply line leak at a coupled joint this joint is normal about at 1/2 tank and if that joint allows air from the tank to be sucked to the fuel pump however this will cause the engine to starve for fuel and quit.
The vacuum could cause damage to the tank. I would check it out.
2007 Tiffin Pheaton 40' DP
2006 Honda CR-V Toad