Why not checkout what they have fitted in the myriad of motor homes in dealers and see what brand they have used , call the manufacturer for a price and fitting instructions
The usual approach is to cut an X in the hoodlining, where the lines extend corner to corner of the internal edge of the interior garnish... which will usually have several millimetres of flange. Fold the four triangles of material out of the way (probably safest pinned back 180 degrees against the main hoodlining). Do your cut in the roof being careful not to ignite anything if hot cutting. A nibbler is best for sheet. Tape up the exterior paint with a thick coating to prevent damage if using a nibbler or jigsaw. Vacuum, blow, vacuum, etc. Install your product, fold the triangles of material back, find the point where they are covered by the garnish, make the cut then install the garnish. If you you need to use spray glue bear in mind that everything in Bunnings now is eco-health-friendly, so entirely useless for gluing anything
Oh, and lay the task out so that you do not cut structure... though it's nice if you can position next to it. An AC will definitely need a reinforcing frame.
The vent I have is 400x400 so how do I work my way around the vinyl metal support rods in place. There are ceiling light wires also in the way any suggestions to prevent cutting wire they seem to be in some kind of duct. Thank you for your help much appreciated.
