I have tightly installed Rmax Polyiso between cathedral rafters, all edges painstakingly caulked with PL300 Foamboard caulk (approx 1/4 inch min overlap to wood and to foil of foam). Btw, the foam is not flush to bottom of rafter, up 1 inch so this caulk is actually in a corner all around – so in other words it’s a fillet.

Now i wonder about adding tape prior to sheetrock in case of long term shrinkage of the Rmax as added protection from gaps

Also have lots of Prosoco liquid flashing left as well as Huber liquid flashing that i could slather on 

Pretty sure all products are compatible after reaching out to the makers

Thoughts?