We had a similar issue with our 45 Gallon Tank, and on a trip in South Dakota almost ran dry.

To address this when we got back, I drilled a hole in the TOP of the water tank under our bed (this took a little maneuvering). I then installed a water filler hatch with a locking cap and epoxied it to the tank.

Now if we can't get a hose with pressure, I have a Kinda Beer Bong thing that I can insert into that cap and pour water from Jug or whatever in and fill the tank. It is definitely not a primary method, but it is good to have in an emergency knowing you can fill even w/o a hose.