best way to smooth and paint door panels?

 i have a set of s10 door panels and i tried to use high build primer to smooth the. it worked great so i painted the panels and a few weeks later the primer and paint came off in a sheet. anyone have any better ideas. thanks  

You should use a plastic prep cleaner first to get any wax or oil off the plastic.  Then use an adhesion promoter to help the primer stick.

t did you ruff them up with? grit of sand paper?

i used wax remover like i would on any car i paint but i didnt use adhesion promoter, thats my problem.  i scuffed the plastic with 80 then 180.