To have that fiberglassed look, First and foremost clean your interior parts first! Any cleaning products will make it horrible fisheye everywhere on you if you do not. I washed mine with dish soap and made sure to get them super clean.
Sanded down with 120 grit, then once that started getting smooth, moved on to 180 grit, then lastly 220.
Wax and degreased the interior pieces (some will say get a specific one made for plastics but I did not) used PPG brand
Spay with bulldog plastic adhesion promoter
Spray with G2/slick sand polyester primer (bondo that sprays) LOL! Fills in the all the groves that I want to get rid of so that it will be smooth like glass.
Sorry I dont have a pic of that step
Then I sanded down again with 220grit
Wetsanded with 600 grit make sure you have plenty of water on the object that you wetsand
Door panels will have to be built up several times to get the smooth look. So be ready to prime, sand, prime sand.
After many hours here is your final product: