Unless you're planning to immerse the sealant, or run very high humidity, many different sealants will do. Beyond that, any silicon sealant that's allowed to cure will be safe enough for a corn snake enclosure. Unlike mammals, they won't nibble or ingest it. For straight construction projects I prefer the GE Silicon II, but the products from Dow Corning are excellent also. IF you are going to immerse the project (bioactive substrate, water pool, planting, etc) then I'd recommend you choose a dedicated aquarium sealant.