I love plasti dip and have used it for a ton of stuff however i would go against using it on the trim... I personally have never done it but i've spoken to people that have and they say its nearly impossible to get all the angles like the inside edges. If i were you i'd just
Buy the vinyl here: http://www.bmwshadowline.com/
And follow these instructions: http://www.bmwshadowline.com/images/ShadowlineDIY.pdf
Since i haven't done it yet i don't know how difficult it really is but from the instructions it seems like it's pretty easy and just requires patience.
Also if you go the plasti dip route and use the glossifier you might not like how the gloss turns out. It's still slightly textured like the original matte black plasti dip unfortunately