Hi Iain,
I've done a few bits and bobs over the years (The PET a few weeks ago which came out perfect and an ST and PC tower case for a friend).
The key is definitely in the prep because even the slightest mark which is almost invisible to the eye will show up and annoy you once you start applying the paint.
Get some decent wet and dry, use loads of water and start with 1000 grade to get the initial years of grime off, then move on to 1400 then finish with 2000. Its worth spending the time on this stage to get a perfect finish, removes all the chemicals which could blemish the paint and also gives a nice key for the paint to grip.
Paint choice, you can go to your local auto supplies (avoid Halfords, very expensive) and grab a can of plastic primer, gloss and lacquer. Personally though I really like the Plasticote stuff, its designed for application to plastic, gives as hard but flexible finish and you can buy it from The Range for about £8 a can, they also do a coloured plastic primer which makes it easier to see you have covered everything rather than the translucent stuff.
Then off yo go, build up the primer in four or five light coatings rather than one thick one, hold the can a good distance away so paint falls as a mist rather than as jets. More 2000 wet and dry once the primer cote is finished to get a nice smooth base. Then apply colour, same again build up in light layers leaving plenty of time between each to dry. Wet and dry between each two coats.
Then finish with lacquer, this is what gives the gloss finish. If you end up with any splodges from the lacquer spitting its no problem just wet and dry again and apply another coat to re-finish. Building up from many light coat will give a harder finish too.
It sounds like a lot of work but its really not. I paid to have the pet done at a car body shop but that was more because I wanted the exact colour match and matt finish which can be a bit tricky to achieve with a lacquer and look good
Best of luck... Im sure it will look spot on
