No as painting inside wont actually stop rust or anything like that. Rust starts from untreated area's exposed to water that iseant waxed properly. Best thing you can spend money on in a bodyshop is getting them to waxoil inside car i.e a,b,c pillers floor,sills behind dash etc etc etc then steam clean underside and do same again especially inside chassis legs etc and once dried a good shutz underneath and job done

IMO ofcoarse