Suggestion: don't rely on solar since there's not enough sun in your situation, instead go for a small generator. It ought to cost a lot less. I've never used one, but know that they can deliver power nicely. Here's an example, but others can recommend a more appropriate one:
Mold may also be caused by the shower, since there will be a lot of moisture in the camper. If you can dry it out during the work day, like opening the top vents (assuming no rain), that might help. I use a dehumidifier at home. Lots of posts about condensation on this forum.