When you are buying that 20 get what is called a 20 long not a regular 20 gallon. That way you get more floor space and a bit less height but it works better for a snake. Also get a good metal framed mesh lid and ask for the metal clips. They come two to a package and are super strong. If you need I can take a picture of ours that have kept a sneaky, determined milksnake in her tank for the last year. Not sure about cornsnakes but our milksnake loves her aspen bedding and does burrow around but also uses her hides (two cream cheese containers flipped over and an entrance cut in....nothing fancy but it works and she loves em!).