Not sure. I think the option I’m leaning towards is the rock wool with the reflective backing and probably a vapor barrier. The metal framing is actually about 4ft apart. I’m not sure how I’m going to make the insulation stay in place.
Roxul makes exterior insulation panels used in commercial construction that comes in 4'x8' sheets. Would be easier to hang than the 14.5x48 peices made to go in wall cavities. Drawback is that big box stores don't carry it, you'll have to order and may have to go through a dealer/distributor to get it.
