Yes I do want to keep the lid. I'm planning a Red Sea 350 in the future, and that will definitely have kessil!
This is my biocube build before the concrete cracked the corner pane. Pics were taken via iPhone6 so the quality is poor. If I recall, I ran them at 60 or 70% with no heating. One thing I did was put some caulking where the wires enter the biocube shield/clear plastic so no moisture gets in. I would do that with any retro kit you purchase, Steves or nanobox.
https://www.reef2reef.com/threads/my-first-saltwater-build.272460/