Adding a zipper to the TT ProTrail fly door

I'm not a fan of the current velcro on the ProTrail and am wanting to use a zipper instead.
First stop was finding a zipper ~127cm long which I have found on eBay (not waterproof), then second stop is to find a business nearby that can professionally install the zip.
But before I blindly go about it can anyone offer some insight into getting this job done correctly?
Or am I on the right pathway already?
Comments greatly appreciated!
First stop was finding a zipper ~127cm long which I have found on eBay (not waterproof), then second stop is to find a business nearby that can professionally install the zip.
But before I blindly go about it can anyone offer some insight into getting this job done correctly?
Or am I on the right pathway already?
Comments greatly appreciated!