I've been using a spraycan product for some time in car restorations, bike rebuilds, etc., for any (non-body) part that I've covered in a glossy color that seems to drastically extend that period of time in which new paint still looks good. It's a clearcoat with really great protection against chemicals, scuffing, and your kids spilling their pop all over the engine compartment.
I'm guessing it's maybe the stuff you alluded to above when you said "wheel coverings." It's a Dupli-Color product called "High Performance Wheel Coating." Comes in various colors, but I've only ever used the clear.
Works great if you get the surface perfectly clean (I use acetone for bare metal prep) and I've not seen any yellowing on parts after three years.