In my s-15 as in most trucks the dash has that texture in the plastic is it possible just to sand down past the texture until its smooth and then paint it same thing with the front cover
you should be able to use high build primer do 2 coats then sand... repeat untill it's smooth. this is probobly the easiest way I know how. most high build primers are very easy to sand. it's a bit like body filler.