The back of my stand sits about 6 inches off the wall and is open. It houses my extra salt, and my ato reservoir. And the wall it sits near is a wall for my fish room. I left part of it open as well. So I can reach under the stand etc. here is a photo from the prebuild.
I don’t because the back of my stand is open too. Plus it is a diy stand that is skinned with pallet wood that has some small gaps between the boards.
If I were worried about humidity I would drill a hole to install a fan.
I run a 4" computer fan in the back. I have an speed adjuster on it because it can be loud otherwise. Eventually will connect it to a humidity dependent switch...