I have boats covered with the same material and finished in the exact same way. I have not had to repair any rips, so can't speak from experience, but I think your approach will work fine. Even if you were not able to reach the repair from the inside I think the PL adhesive applied over the outside would suffice. The patch on the inside will make it even better.
There are probably other ideas and methods and I'm anxious to hear them - I'm sure at some point I will need to do some repairs also.