Neal.
I paint with solvent based paints - so you don't need to do anything to the inside really.
That said I've tried plasticote clear spray - and on my own shells I tape up the parts that will rub on the chassis with a kind of white gaffa tape. If you search eBay I think it's called 'glass' tape or 'cricket bat' tape.
Super strong and stops paint getting scratched off
