Hi Matthew,
While I have not used the Advanced Graphene Coating on a convertible top or tonneau cover, I have used the Ceramic Spray and Graphene Spray coatings on both. The results have been very good and the longevity is excellent. There are threads from me on the Mustang, F-150 and my Colorado that show the results.
As for the application, make sure the top or cover is clean and completely dry. Do a small section at a time applying the coating with a Gray Microfiber Applicator. I go over the section using two patterns, north-south, east-west to make sure everything gets covered. This is where it gets to be a bit of a challenge and that is seeing it rainbow or flash, so you need to pay attention and look from multiple angles.
Once it flashes, then I used a borderless gray towel and vigorously go over the section. Then start by putting the coating on the next section. Don't try to go to fast or do too big of a section and be careful not to get the coating on anything other the top or cover itself. Blue painters tape works well to protect the rear window on the top.