I'd like to put this on top of my deck. What is done for a base floor? Does it need to sit on poured concrete?
When placing on a deck, it is common to lay something on the deck boards that will prevent air from flowing through. This could be something like a piece of vinyl flooring, cut to the size of the sauna. The cedar duckboard floor that we provide would sit on top of the vinyl.
The answer to your second question is that the outdoor saunas do not need to sit on concrete, just a strong base that won't allow cold air into the sauna room.