i wouldnt use duct tape. it will just become a sticky goo. not sure what chemicles would be off gassed into the room as well. always use the temp gun on the substrate in the enclosure to know what temp the snakes are actually seeing. not what just the tubs are seeing. you will notice a difference.
as far as the difference in temps go. make sure all the pieces are the same exact length and that the connections are solid.
adam jeffery