I have to agree with John, I wouldn't put any heat in a humidor, unless it was humidified heat, and for that matter I wouldn't do that either. Keep this in mind, a freezer is already insulted to keep cold air in, works the same to keep heat in...if the ambient temp is say 68 degrees all the time, one would expect it to stay that way, unless you are constantly opening and closing the unit to check on things. If you don't already have a remote hygrometer for this freezer, then get one. Oregon Scientific units are available from cigarmony.com, a vendor here on the board, this will prevent you from opening and closing the freezer to check temps and RH. Just a thought, hope it helps.
Rob