To bypass the water heater, there is a round access cover under the mattress. It is directly over the rear of the heater. No need to remove the plywood that the bed rests on. Reaching in there you will find the back of the water heater. There are 3 valves. To bypass, the lowest and highest ones should be closed (perpendicular to pipe) and the center one open (parallel to pipe). To use the water heater, reverse settings.
If you want to run the sanitizing chemical through the water heater you could just let the water pump do it by opening a hot water faucet and running a lot of water. Maybe when done then just remove heater drain once to help get all the chemical out of the heater, or just run lots of fresh water through it by opening hot faucet.
2012 Forest River Sunseeker 2300 Chevy