I'm making a template to have a windscreen cut for my 3 wheeler. I've fitted the seal to the aperture and have cut a cardboard template and fitted it. when fitted, I drew round the inside of the seal onto the car so I know how big to cut it.

What I don't know is how much gap I should leave between the glass and the centre bit of the seal. Is 1mm all round enough or should I allow 2mm?