If you leave solid you will want to run an air pump for oxygen exchange. My 7 gallon aio I had glass cut to fit on top. Back chamber cover has corners cut and a slit for light mount which is kind of to small. I put air pump with stone in first chamber in the sock. I never had heat issues this way sealed. Make sure there is also enough room for gas and air to escape. So if you have to drill, drill 2 holes. One for air line one for air and gas to exit. This will also stop 99 percent evaporation. I no longer have to top off the tank every day. It is stable till water change each week.
Having more holes allows for easier surface area gas exchange but also more evaporation.
What are you looking to accomplish? Keep things from jumping out? Slow evaporation?