There are a couple ways to do a bypass of your water heater, but the idea is the same in all cases. You need to have a way to stop cold water from entering the water heater, and you need a way for the cold water (or antifreeze) to make it to the hot water faucets.
In this photo, you can see a valve at the bottom of the tank at the cold water inlet. This is a three way valve, in one position it allows water to enter the tank and blocks the water from entering the jumper hose between the cold and hot water pipes. In another position, it blocks the cold water from entering the tank and allows it to "bypass the tank" and continue on to reach the faucets throughout the camper.
Another (more common) method is to place valves at the cold water inlet, the hot water outlet, and midway on the bypass hose. Closing the two way valves keeps liquid from entering the tank, and the open valve on the bypass allows it to go by. Closing the bypass valve and turning the other valves puts the water heater into the path of the water.
Hope this helps.