On Sunday, 17 March 2019 14:12:04 UTC, JimK wrote:

If you are plastering walls around the opening then you can apply
plaster direct to the lintel just press the initial bonding coat into
the gaps to maximise adhesion.
I wouldn't do that as if the rest of the ext walls are insulated
the reveals will become the coldest place = condensation, mould
etc.

Yes, I am keen to ensure there is at least some insulation around the reveals (although the door frame width means there won't be all that much).

I also don't think plasterboard adhesive necessarily sticks well
to the insulation of insulated plasterboards.
Depends what the insulation is faced with ? Paper? Foil? Foam?

I'll be making my own plasterboard+insulation sandwich and so it'll be foil backed. I too had read that dot-and-dab adhesive doesn't stick well to it, but it seems that most 'tube' adhesives do.