I'm an inexperienced airbrusher in search of advice about Floquil. Is it correct that Floquil will damage plastic unless it is first given a barrier or "primer" coat of non-Floquil paint? If so, is it possible to use Floquil to weather unpainted plastic trucks and couplers without first applying an undercoat? Thanks for the help. All advice - no matter how basic - would be welcome.