You seem to have fairly regular gaps to scribe. Not sure if you have a table saw but that's where I would start. I cut strips that are as wide as the widest part of the gap. I like to put a little angle getting smaller away from the face on the wall side of the piece then it's a little easier to plane where you need to make it smaller.
If you then hold your piece upo against the inside edge of the cabinet and take a block of wood the same width as the cabinet, run that block down the wall marking any movement in the wall onto your scrim piece and use a plane to trim it to that mark. You can fill any small imperfections with filler.
Lots of different ways to fix it in place, none of which I want to describe in public! Just get away with whatever works. Glue on the edges and tapped into place will often do.
You can even tap some pine strips into the gap and plant some plasterboard on top, it's easier to scribe.
You would hopefully be looking at very small gaps so decorators caulk would be the quickest option. Larger gaps kind of depends on whether you're likely to get movement between the materials. Something flexible is probably ideal.
You seem to have fairly regular gaps to scribe. Not sure if you have a table saw but that's where I would start. I cut strips that are as wide as the widest part of the gap. I like to put a little angle getting smaller away from the face on the wall side of the piece then it's a little easier to plane where you need to make it smaller.
If you then hold your piece upo against the inside edge of the cabinet and take a block of wood the same width as the cabinet, run that block down the wall marking any movement in the wall onto your scrim piece and use a plane to trim it to that mark. You can fill any small imperfections with filler.
Lots of different ways to fix it in place, none of which I want to describe in public! Just get away with whatever works. Glue on the edges and tapped into place will often do.
You can even tap some pine strips into the gap and plant some plasterboard on top, it's easier to scribe.