Hi, so are your saying don't worry about if moisture gets to the insulation?
TBH the wall doesn't feel that damp over the years as it's been like this for a while. As long a breathable I don't think damp will be a big issue.
I have an old small barn I'm renovating into an annexe.
It's a 9" solid wall which has been previously framed out inside.
Thinking of two options for insulating the walls
put 50mm pir between studs behind ladders/noggins and 50mm attached to the back of the frame in space for cold bridging...