SEM brands make a prep spray that is very useful when painting vinyl and
plastic interior parts. It chemically " cleans" the part and lets the paint
adhere much much better than just spraying the paint on. You may have to
go to a shop that sells paints and paint prep products to body shops and
such to find it. It can be found in spray cans as well as in bulk as I
recall and its not expensive.
Mikey
62 Crown Coupe