I did not use any primer on the plastic shell. I immediately painted it once I put out the shell from the box I received from Sharpe way.
When prepping for a spray paint, don't be cheap and use quality stuff especially when it comes to the scotch tape. I used the 3M professional green tape designed for paint jobs. Other scotch tapes may peel off the original paint job. Make sure you seal as tight as possible. As you can see the second photo there are still white paint.
I sprayed the entire shell with green paint except the black and red area. I hid those areas using scotch tape. Spray the paint very fast to avoid excess paint at one area.
Be patient. Wait for the paint to dry (takes about 3 to 5 minutes depends on how much paint you applied. Do all the spray paint outdoor as the spray paint is toxic.
Always use a ruler to paint the trims and door handles. I didn't use the ruler at first. You can tell how crappy how area looks like. I painted the window area with a black sharpie. Too bad I didn't use a red sharpie to paint the buffer area otherwise it will look better.
I may get another one later and paint the stripes with yellow. That will have to wait a bit.