I agree with Melinda regarding the thermostat. Cheap ones work OK, until they don't, and then you'll wish you bought one that is known to be more reliable. Herpstats are very reliable; I use many of them.
I don't keep corns, and I respect Melinda's knowledge, so I'm not trying to disagree with anything she says. A 20 long seems to be the (bare) minimum recommended caging for a corn, and lots of folks here don't think that aiming for the minimum is ideal.
If your snake grows to a larger than minimum size, and if it wants to test its caging, a 'proper reptile enclosure' is going to be best, and perhaps even necessary. Screens and snakes don't always get along -- a snake that rubs to test its enclosure is going to have a health issue (rostral abrasions) in a screen top cage.
A 'proper reptile enclosure' is one like this:
https://apcages.com/collections/terr...6l-x-24w-x-12h
I think Melinda's point was that if/when you find that a critter cage isn't quite ideal, this is the sort of enclosure you might consider. I hope that if I'm reading her wrong she puts me in my place.