If you coated 'em with mold-release, and then foamed in with the spray foam around them, that might help. But with side openers, you're always letting a lot of the cold out when you open the door. How I'd try to address that is with a large piece (to fill the opening) of medium weight clear pvc material (as in dodger
windows), with a bolt rope
sewn to the top, and slashes every 2 inchces or so, so that you can reach in through it. I would reinforce the top of the slashes with a strip of the same material, glued on with pvc pipe glue. You'd mount bolt rope
track on the top of the inside of the enclosures, with enough room to feed in the sheet. We used to use this in the US in grocery stores to keep down power usage, but it seems to have fallen out of favor.
Or perhaps add another solar