I am currently building an Octagon sauna that will double as a mobile bug out shelter that will be mounted on a trailer.
I'm putting the octagon on edge if you can imagine so that when viewed from the front or back the octagon shape will be apparent.
The design will be 2x4 construction and I was thinking about cedar on the inside with a plastic vapor barrier then foil backed foam 1 1/2" foil facing in then a second layer foil facing out then 1/2 inch air gap then plastic vapor barrier then pine t&g outside. The 1/2 air gap will be vented to outside air. With vents both top and bottom
I was considering rock wool or fiberglass but I'm not a carpenter so I need some advice.