What size enclosure LxDxH? Depending on your home temps you can go by the Wattage CHE you need for now.
As others have said you cant beat a Herpstat2. Then you can control both heating units, set it & forget it. A Dimmer will change depending on temps in your house. If the house is 70 and your Heat Mat or CHE is running at 90 it can change in a flash if its a nice day and your house gets up to 76... Suddenly that 90 can become 98.