You need a paint specific for lexan so it can flex and wont crack. Pactra has a big assortment of spraycans and airbrush paints that are easy to work with
RC lids (bodies) are also painted on the inside. A good practice is to clean the inside of the lid with dish-washing soap and thoroughly rinse it. I also like to rough up the inside of the lid with a green scratchpad before I wash it to give the paint more surface are to bite on.
Lots of thin coats is the rule and when you're done spraying color, back it with something like Parma's FasBlack paint.
I use Parma paints as well as Pactra. Here is a totally rattle-can paint job that I did a while back:
I try to support the LHS with smaller purchases like this. If there is a specific color I want that they dont stock than Ebay will typically have what I need. It kinda depends on how set you are on a color scheme. I will typically have an idea when I go there but sometimes modify it depending on what they have in stock.