I've also done trim with a hot air gun its a case of diminishing returns the surface get more and more prone to weathering so you end up painting them in the long run. Bumper/trim paint from rustoleum and plastkote is good long term. Short term I've found that plastikote bbq paint is a good solution for black plastic that lasts a couple of years, simple to apply, simple to remove, simple to touch up, flexible. Originally I had the end of a can and decided to try it on rear door step trims. Found you can wipe it on with a sponge or lint free cloth with some thinners so no need for masking, when it gets damaged or scratched you can wipe on some more, no worry about overspray etc.