[bstark]

The biggest reason they install those things (most RV builders) is to prevent the pressurization of the entire incoming cold water system. Pressure can now back up the incoming line and add pressure to your entire cold water side. Maintaining a "head" of air in the hot water tank by periodically draining water out of it and manually opening the "pressure relief" valve to allow the vacuum created by draining water to pull some air into the tank to re-create that "head" will help reduce the back-up of pressure into the cold lines without that check valve. A PITA but doable.

Draining that tank is something you should be doing on a periodic basis anyway to prevent build-up of calcium/lime and to check the staus of your anode rod. It goes very quickly if once you remove the anode rod you stand well to the side and lift that little lever on the pressure relief valve allowing air into the tank.

You'll be surprised at the chunks that come out of there.