Obviously strip the interior out first.

First off, scrub the plastic bit down with Prepsol (AKA Wax & Grease Remover)


Next, spray it down with Flexi Primer.


Once its dry, it'll look like this.
If the surface is a bit rough: put down a coat or two of Spray Putty over the primer. Once dry, lightly sand it using 600-800 grit Wet 'n' Dry for a smooth surface.


Wipe down the dried panel with Prepsol again.
Now put down the base coats. In this case, matt black.
The backing colour will effect the final colours appearance. Black gives darker results, white gives lighter. Experimenting can make for some cool effects & blends.


Once its dry, on goes the colour layer. In this case its a flip. Not much to look at yet.


Finally, when its dry on goes the clear coat. This makes the paint "pop" and gives it its gloss. Here it brings out the flip effect, the photo's dont do it justice.


Thats it ! Once the top clear coats dry its ready for action
Your new painted interior is heaps easy to clean, a quick wipe with a moist cloth is all it needs. Maybe some Meguires Wet Look on show day.

FAQ:

How many coats do I need of each ?
As many as you like. As a general rule of thumb however:
Flexi Primer - 2 coats
Spray Putty - 2 coats. Possibly more if the scoring is very deep
Base Colour - 2-3 coats. Enough to cover the original colour and/or spray bog
Colour Coat - 2-3 coats. This is dependant on you, more coats will give more intensity. Start with 2, and add more if you desire more intensity in your colour (remember, this is what everyone will see)
Clear Coat - 2-3 coats. Again, this is up to you. More coats mean more gloss, but it also means you should sand between coats

Glossary:

Base Colour - The basic colour that your colour coat is sprayed over. It will effect the final colour, so choose wisely.

Clear Coar - Transparent lacquer that adds gloss to your colour coat, seals & protects the colour coat.

Colour Coat - The is the final colour that you are laying down, and the one everyone see's. So make it smooth & even !

Flexi Primer - A primer designed specifically to promote paint adhesion to plastics & nylons. It is also designed to be flexible, to prevent cracking & crazing when plastics move & settle

Flip - Colour changing paint. Also known as Kamelleon & Chromallusion

Matt - low gloss paint finish

Prepsol - Preparation Solution. A liquid cleaner specifically designed for cleaning painted surfaces ready for additional paint applications or for waxing. Also good for removing bugs & tar.

Primer - A base layer that promotes adhesion between paints (and also putties) and different surfaces

Putty - A dough like material used to fill cracks, holes, etc. Also known as Bog or Nicky

Spray Putty - A very thin putty that is applied similar to sprayed paints.

Wet 'n' Dry - Very high grit sandpapers which can be used dry, or with water (wet). Wet sanding gives a smoother finish but also takes longer and requires drying time

xxx Grit - Measurement of sand paper courseness. Higher numbers = finer grit, which in turn means finer finish