Krylon "Fusion" hands down for painting anything plastic on an RV.
I picked up a TT real cheap that had yellowing on each and every plastic part from the porch light cover, window frames in doors, fridge vent, stove vent etc. made the whole TT look old and tired.
I used Krylon Fusion on each and every plastic part and the TT looked brand new. Dries in seconds too!
I flipped that TT for twice+ what I paid for it! The people that bought it still have it and 6 years later and the white is still as white as the day I sprayed it on.