solved the problem myself.
Cut the fabric behind the arm-rest up behind the back of the seat. Also cut two slots in the lining on the seat back in the boot. I then used self adhesive velcro on the metal seat back and stitched to the fabric and liner to ensure it could be tucked back into place. It works fine. Just need to find some thin rubber or plastic piping that I can run around the edge of the metal so it doesn't scratch the skis and it's sorted. Maybe not as elegant as a plastic hatch that can just be popped open, but good enough for occasional use.
Cut the fabric behind the arm-rest up behind the back of the seat. Also cut two slots in the lining on the seat back in the boot. I then used self adhesive velcro on the metal seat back and stitched to the fabric and liner to ensure it could be tucked back into place. It works fine. Just need to find some thin rubber or plastic piping that I can run around the edge of the metal so it doesn't scratch the skis and it's sorted. Maybe not as elegant as a plastic hatch that can just be popped open, but good enough for occasional use.