Thanks for the replies! Reinz do you use a RHP in your pictured enclosure? I have no doubt that RHP's would be great in this application but I'd rather not use them just because they are so much more expensive than heat tape and I already have a bunch of heat tape laying around. Cost is definitely a factor in this project. The sandwiching idea sounds pretty sweet! Let me know how it goes and I'll give it a try.

Anyone have any recommendations on soil type and depth? Is too much humidity a concern here with the plants since Carpets are a lower humidity species?