Perfect Wall for Park Model, Followup – GreenBuildingAdvisor

This was the proposed assembly :

1/4″ Wood T/G decorative planking over 2×4 studs

Smart Membrane Vapor Barrier

R-15 Rockwool Batt 

3/8″ exterior ply sheathing w/ WRB (eg  Benjamin Obdyke Hydrogap).

1″ Polysico or XPS foam board over WRB exterior.” *

3/8″ air, water gap as rain screen drainage plane

3/8″ Siding

After doing further research I noted that some folks use GPS (Nucor) Type 2 Rigid form board because of its better permeability (3.1)  for drying than XPS (nearly impermeable).  As it will also serve as the rain screen behind the cladding I am unsure of which is better and if the GPS should be faced or left plain. 

Am I overthinking this?