Great post, thanks!
Recently did mine with the 3M kit, but couldn't find anything definitive on what to protect them with, other than the uber pricey German 2K product, which is not available locally. So, I decided to try Rust-Oleum's American Accents Clear (which does not declare if it is acrylic, enamel, or other on the label....). Almost immediately, it started to crackle, looking like a piece of alligator hide! Went back to square one, had to use 80 grit and a palm sander to get off the finish, and start the polishing process over again. This time, before spraying the clear, I prepped the surface with Dupli-Color (Auto Zone) Adhesion Promoter, 2 coats. I followed with 3 coats of Rust-Oleum, and it made a huge difference. No crackling or spidering! Clearly, the plastic lens surface needed to be prepped to accept the clear coat. https://photos.app.goo.gl/upvGfvWPHKzg3O6B2