solar panel

Hi all, I have a 2018 Bailey Unicorn Vigo and have been having a couple of electrical problems - it has a solar panel. The 1st symptom was the motor moving not having enough uumph to move the caravan - I disengaged the motor mover and tried operating it without 'load' and the mover gear rotated...

So I'm moving our van from an area that has power to a stores with no power. The alarm would be set, bit nothing else will be running. What is a simple solar panel that I can get just to set up when not in use to keep the battery charged please?