Hi,
I agree with Pavel, the exhaust can be a problem.
There are a few other things to consider.
1. Why the Zip?
I know that my original roof had no zip. Really scared the crap out of me one day when the 998 hit 110kph
with no doors, the hood acted like a parachute and the back end started to lift.
My first attempt was a a zip either side with Velcro across the bottom. At least if there was enough pressure, the Velcro would seperate and allow the wind out.
2. Why the zip?
For access it’s a personal choice. It looks cool rolled up, but is open to be blown around by the breeze.
Also, if the zip is low, it’s a pain to undo when the spare wheel is fitted.
So really Jim, ask your self over and over, why the zip?, and look at how you would use the window opening, is it for flow, is it for access, is it purely asthetics?
This time around I had PRU’s rear window zip higher up, like above the back seat. So much easier, but another suggestion ( that came up after) was to zip it down and roll the window down behind the seat, or down into the boot and strap it down.
Look at lots of roofs, there are so many variations, and everyone has their own good reason for doing a particular way.
HP