A pondliner usually covers it. The part of the basement where this setup is at used to be a garage. I run dehumidifiers in the house, but I just let this room do it's own thing. I would think if there was an issue then you'd see it on the windows.
LOL, IF I had the room this thing would be set up on about a half dozen 55 gallon drums as vortex chambers. I'm limited on space too, I'd just rather stack tanks on top of eachother then cramp the filtration. I need to be able to work on stuff. Most of my systems are setup with double stacked tanks and filters off to the side so I can mess with them.
Why add volume? I'm sure there's improvements you can make without increasing volume, or increase the volume in the same space.... There's usually a way if you want it enough. Most people set stuff up and call it good, I like to improve.