[PeterAllen]

Thanks for the replies, much appreciated.

Some are a little off target so I probably didn’t explain the issue correctly in the first instance. I’m looking at two issues here. First is gluing the fiberglass rear window section to the shell which is achieved by applying Sikaflex in the pattern shown in red and pressing the section to the roof. I'm confident the Sikaflex will do that.

Once that has cured I then need to blend the edge of the fiberglass section (shown in yellow) to the metal roof with bog or ???? Whatever I use it needs to withstand the movement variations between the fibreglass and metal roof the Sikaflex will allow without itself cracking.

Others have tried bolting the fiberglass section to the roof but invariably the fiberglass will crack around the securing fasteners, hence the use of Sikaflex which itself enables cracks to appear in the joins… “There’s a hole in the bucket dear Lisa, dear Lisa…”