I thought of the bypass valve also, because its the only thing that can be changed in the water system. But I don't see how that could matter, as the bypass valve prevents water from going into the water heater, so you can then put in RV antifreeze without polluting the tank. I think I'd look at it (its at the inlet to the hot water tank) anyhow.
Beyond that, I'm stumped. The cold water should be separate from the hot water, and I don't see how it could have suddenly changed itself- its plumbing, after all, and plumbing can't change itself, because it can't hold a pipe wrench.
Interesting regional terminology (and I've seen it on here before)- around here, a "camper" is mounted on the back of a pickup. What you have would be a trailer. What do you guys call a pickup mounted camper?