As far as the propane guage, it might be the plastic guage sending unit. Take it off the tank and go see your local propane distributor. (It should be a magnetic, so it does not penetrate the tank, attached with 2 little self tapping screws to the main sending unit which does penetrate the tank) They should have them in stock. I know Heritage Propane has them, if they are in your area.
If you are not sure about this, take the whole motorhome to them and let them take the sending unit off.
2003 GMC 2500HD 4X4 D/A Ext. Cab
Propane Powered Honda EU2000i
Lots of Hot Sauce!
Air # 283