This is good additional information! You had only mentioned that you were looking for Solar to keep battery charged, during storage.
The easiest fix, would be to get two AGM Batteries and move them into the occupied area of your camper (In a cabinet, as I did). Batteries will lose considerable capacity when the temperatures drop. Having the AGM batteries in the heated area, would increase your battery capabilities, during colder periods.
There is lots of discussion on the Pros and Cons or the Flat Solar Panels (Flex or Film), but what might impact you more, is that you would not be able to take advantage of the low to the horizon sun’s position in the Late Fall into Winter time of the year, if you are attaching your solar to the roof, thus unable to tilt your panels.
Yes, a space case can take up some room. But, how many panels are you planning on putting up there? You could put your space case in the middle and then install two solar panels, one on each side of your space case. This would allow you to take advantage of the sun as it travels, negating the shadow across one of the panels, for a percentage of time.
I love my solar, but there are other options that should be considered when cost and amount of time of use, are added in. If you have the funds, do it all.
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