Solar is definitely a good idea! I have a modest system on my Windsport - a 100 watt Renogy panel kit, permanently mounted to the roof. Like you, my RV sits idle and unconnected to power for periods. Since installing the solar panel, my batteries (2 each, 6-volt golf cart in series) stay nicely charged. I like having the system installed permanently, so I never have to fiddle with it.
Here's a link to a Renogy panel kit - this one has a different controller than what came with my kit a few years ago, but it works well.
https://www.renogy.com/renogy-100w-12v/starter-kit/