It looks like it will be totally enclosed. Many people that use this type of system use radiant heat panels. I am not sure where you can find them overseas. As for the substrate I am not sure on the one you listed but I have had experience with cypress mulch. Again I am not sure what kind of stores you have locally but it can be found in a gardening type store. Just make sure there is no additives. The cypress mulch can be misted with water and will hold moisture for long periods of time.