Depend on how the trailer was winterized will determine the amount of air in the tank.
If your system has a bypass valve and that valve was used to shut off the hot water tank and then the tank was drained you will have 6 gallons of air in the tank when you first turn the water on and open the bypass valve.
When starting in the spring open the bypass valve and connect to city water or fill the system form the fresh water tank with the pump. After 3 or 4 mins. open any hot water faucet and bleed off the air. Close that faucet and let the hot water tank continue to fill. Again after few mins. open open a hot water faucet. You will have to do this untill you no longer get air from the faucet, that faucet should be the furtherest form the hot water tank.
Do not light the hot water heater until there is no sign of air coming from any faucet. Lighting the heater early can cause a blow off from the safety valve or in an extreme case could melt the side walls of the tank.
WBCCI 12156 AIR 3144 WACHUNG TAC NJ6
2004 Excursion 4x4
1991 34 ft. Excella +220,000 miles, new laminated flooring, new upholstery, new 3200 lbs axles