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...
On my TC the solar panels charge all the time through the charge controller. That way the batteries are always in tip top shape. No danger of ruining them if your controller is working properly. If you don't have AGM (sealed) units then just keep an eye on your water levels.