I have a cedar AH barrel sauna with a Harvia 6kw heater that has not been connected yet. I am looking to add a "rain jacket" / waterproof tarp but am concerned about flammability of tarps. From my understanding, the AH rain jacket can be left on when the sauna is in use and it is water-resistant but not waterproof. It also costs a lot more than buying a $15-$30 tarp and securing it yourself with eye-hooks. I have looked into flame retardant poly tarps which are waterproof.
I would like to know from barrel sauna owners or other that have experience with them, what is the max exterior temperature of the wood on the top half of the sauna?