IBC work perfectly well for small set ups and are a great upcycling use (as long as you know what was in them first!). Having them in the cellar is fine as long as precautions are taken. Foil on floor trusses definitely doesn’t hurt but there is no substitute for proper ventilation, if the lids are preventing moisture from escaping the tanks then they are also preventing gas exchange between the water and the atmosphere. If they are are loose enough for proper gas exchange then they are loose enough to allow moisture out. Even a single medium size aquarium with a lid can cause mould problems in a room with out good air exchange, I found this out the hard way, a long time ago, as a teenager, in my bedroom at my parents house!