Bought my used camper last year and a solar panel was already installed when I got it. My last camping trip I ran the heater overnight for two nights with no problems and was camped under trees so do...
Controller will provide a very small but persistent draw on the battery even when off. A second switch between the controller and battery is good if stored without power for an extended period. Use the panel switch first. Many controllers can be damaged if fed solar power and not connected to a battery. Connected to a battery and no solar is no issue or there would be trouble every night.
For all the effort I would look at a new controller if this one does not operate as expected.