Never put antifreeze in fresh water tank. Im not sure where you found instructions to do that, immediately delete that content, any bookmarks to it, and don't listen to anything else that person, site, manual ever say again.
How do you bypass your water heater? You have to get back there to do that no matter how much of a "pain" it is. You may be much better off having an RV service/dealer do this for you. Money well spent and much cheaper then the alternative.