Flush the water heater tank by removing the drain plug (Atwood water heater) or anode rod (Suburban water heater) and running fresh water out of the drain hole until the tank is completely flushed. If no water comes out of the drain hole then the diverter valves are set in bypass mode. Correct this by turning any valves at the back of the water heater in the opposite direction. Install the drain plug or anode rod and fill the tank. Do not start the water heater until you are sure the tank is filled and open a hot water faucet to bleed the air from the tank.
<Good anode rod
<Bad anode rod (replace)
Flush all the plumbing lines with fresh water by opening all of the faucets one at a time until you are sure the lines are completely flushed.
Check thoroughly for plumbing leaks especially because mice have been plentiful this winter and like to chew through RV plumbing.
The roof should be checked for winter damage at the beginning of the season and seams should be re-sealed if necessary. Do not use silicone based sealant on a rubber roof because it will not stick for long. Always use a rubber roof sealant such as Dicor brand rubber roof sealant.