We have solar panels on our RV roof but we did purchase a Renogy 100 watt suitcase 5 years ago as we often find ourselves in shaded sites. Our Renogy solar suitcase is solidly built and has endured all kinds of extreme weather over the years, although the original controller gave up the ghost during a monsoonal downpour a couple of summers back. It was not water proof, went to their website and purchased another controller from Renogy with water resistance capabilities.
Can not comment on solar panel efficiency degradation while in use versus stored, we use our Renogy solar suitcase sporadically as well, have not noticed much deviation in panel performance as it pertains to output voltage or amperage. Does a great job supplementing our rooftop solar, or all by itself as we can track the sun all day for maximum efficiency. Lent solar suitcase out to a few friends and family members, they were impressed and have since purchased their own.