I am trying to design a simple but robust, adequately insulated wall for a shed that will be used fairly regularly in the winter (Ottawa, Ontario)

Gyprock
Strapping
2x6 Roxul
Plywood sheathing (taped - also functioning as air barrier)
Tyvek
3" Comfortboard IS
Strapping
Siding

Any opinions? This is not a lived-in space so I don't want to go overboard on insulation. The moisture load from the interior will be very low, but I am concerned about the sheathing getting moldy from exterior winter air.