Hey Bradley! If your deck is not untreated wood, e.g. if it has a sealant on it or if you have a composite deck, then we do recommend you place a layer of untreated plywood or tile on top of the deck in the area where your SweatTent will be set up. This will protect your deck from scratches, marks, etc. and it will ensure that no chemicals are off-gassed from the treated or composite deck at high temps.
Please let us know if you have any other questions. We can't wait for you to experience the Sweat Tent :)