Hi AJRV re the water fill problem.
Option 1. Get a relatively thin and hollow plastic tube and fit one end with a small floating device ( a bit of cork etc) cut the tube long enough to float on the inside of the tank and leave 2-3 inches outside. Then insert the water hose beside the tube and fill. The tube allows the air pressure to release and fill float up as the tank fills.
Option B. Fit the top of the tank with a air release valve - same type of device as in the back of most portable 5 gal gas tanks. In this case one would have to reach in and open the valve when filling the water tank.
Good luck.