Unhook all waterlines. Unhook LP line. Remove all fasteners along outer edge of tank, on outside of the coach. Pull tank assembly out of coach. It will be a tight fit, if you cannot get it out, check inside to make sure plumbing is not caught on any part of the tank. It is a tough pull to get it out. I am assuming you have an older water heater that does not have any electrical connections. If not make sure they are disconnected before trying to pull tank out.
2003 GMC 2500HD 4X4 D/A Ext. Cab
Propane Powered Honda EU2000i
Lots of Hot Sauce!
Air # 283