I would think that opening the water heater bypass valve would be a poor solution at best. Think of water flowing towards wherever there is low pressure. If you opened a cold water tap, hot water would flow into the cold water side. If you open a hot water tap, cold water would flow to the hot water side. This is not a permanent solution, as you would have to open the bypass valve each time you wanted to use the hot water, and then close the valve. Installing a mixing valve is the best idea. I read somewhere that many trailers come with one, if the water temperature at the water heater is not adjustable.
2015 Starcraft Travel Star 299BHU Black Pearl Edition
2011 Jayco X23J (traded in)
2009 Ford F150 FX4 SuperCrew