It shouldnt peel off that easy unless its not enough coats/ you've left open edges for it to lift from (if that even makes sense, it does in my mind) but you're using it for a rally car so I could understand it peeling off easily as it gets more abuse then a daily driven road car..
I did my wheels and wing mirrors over a year ago now? And theyre perfectly fine to this day, only thing was the wheels had to be touched up after the tires got changed(understandable) and theres maybe one stone chip on the wingmirror which went through the plastidip but the paint underneath is fine.. I know its not much of a comparison to a whole car being done but its some insight I guess..
oooh and pick your colour wisely as some dont suffer to well when they get dirty...