
"And none of my 3 Avys ('05, '09, and '11) have ever leaked a drop in the bed."
Either you never take your truck out in the rain, or you have some secret that I need to know. I don't get leakage up at the front end (of the back covers) nor down either side, but a hard rain will encroach (for those of you in Georgia) that means it gets wet inside via the seal between the back cover and tailgate. 
Must admit your black panels look super. Are you saying (refinish restorer) is a product you are treating the black panels with or is it a spray paint application. 

again...
Actually, none of my three Avys have ever been in a garage. They have all always sat outside in the weather. And none have ever leaked into the bed. Don't know why, but they haven't.
Refinish Restorer is a product by CarWorx, a German company. It is amazing, and is available on Amazon, where I bought it. I used less than 1/4 of the product in this quart can, and I did all of the plastic twice. It should last me for the rest of my life! I applied it with an old washcloth and let it dry overnight between coats. It requires no buffing or anything... just let it dry.
There is a long thread about RR on the Avalanche Fan Club forum, with many testimonials and pictures. Folks there say two coats have lasted on their Avys for years. It's an oil-based preservative that the manufacturer claims soaks into the plastic and forms a seal coat on the top. It sure made my Avy's plastic look better than new, and totally got rid of the "tiger stripes" on the sails AND all of the chalking.
Edit for full disclosure: OhioBellBoy (Mike) introduced me to Refinish Restorer. Thanks, Mike!
Ken