Hi Im just south of Austin, so zone 2a,  I just built a workshop, with a vented cathedral roof (for loft storage), I havent installed any interior drywall/plywood  yet so the studs are still exposed.

I just recently found out about a local seller with reclaimed 2″ polyiso, with a fiberglass facing on each side, at a very good price. I price I wish I had known about before building, so I could have done exterior insulation.

With my current setup (below) is installing the 2 inch polyiso to the interior studs, on walls and ceiling, going to create any problems moisture wise?

From the outside in. Roof (2×6 rafters):
Galvalume corrugated metal roof
7/16 zip sheathing (taped)
1 inch air space
1 inch of EPS foam as baffle
3.5 inches Fiberglass insulation

From the outside in. Walls (2×4 walls):
hardie lap siding
3/8 rain screen gap
7/16 zip sheathing taped
3.5 inches Fiberglass insulation

I plan on adding drywall to the ceilings, and plywood to the walls (its a woodworking shop).

Any insight would be greatly appreciated.

I know the r values still arent up to standard, but this is a workshop, and I only really use it during the colder months here in texas. Im in Montana for the summers. But getting another r12ish seems like itd help, if there arent an drawbacks.

Thanks
RG