RAGGTOPP Cleaner and Conditioner has worked on several hundred convertibles I Detailed in the Pacific Northwest, and turned all of them into beautiful, striking, totally protected from rain, convertible tops...
I used a more involved method because I have the machines - I pressure washed the top to start, then applied and scrubbed in the cleaner with a brush, then pressure washed it off, then rinsed again and extracted using my Mytee HP60, then blew it dry with the Master Blaster, let it dry really good and applied the Conditioner the last part of that day or the next day if I still had the vehicle...
Never had issues, everyone had great comments regarding how nice their tops looked now; its good for a season if the car is out all the time...
Good luck !
Dan F