How to close patio door reveals

[akist]

As on the photo, I have used a plastic cavity closer around the patio doors (and windows etc).

I am not sure how to construct the reveal, as the plastic cavity closer is flimsy, and just sticking plasterboard over it will likely fall off. Maybe screw the plasterboard through the plastic closer and into the blocks?

 

[jeds]

Cut the closer back so three quarters of the block is exposed and dot some insulated board onto that.

Also seal the closer to the blocks with some good silicone adhesive and few more nails..