I made my own cos the template I was supplied was a) Crap and b) made from thick cardboard and didn't bend.
The seal was 9mm thick so I went and purchased a piece of timber from Wickes that was 8mm thick, put masking tape in the roof, taped the glass into position and drew around it with the 8mm spacer then cut out the hole with an air saw which has got a small 1mm thick blade, de-burred it with a half moon file and then fitted it