Hi Paul
I use that White Knight Rust Guard Epoxy Enamel available in most hardware stores. At times when I need a special colour other than what is available in the White Knight range, then I spray an over coat of clear Wattyl Estapol.
I also use Estapol over tissue that has been first painted with Aeroflyte dope, but I have heard of others using clear 2 pak poly eurethane. eg The Linwoods use that.
I think most of the F2B guys that I know from Sydney use 2 pak polyeurethane auto paint on their stunt models.
I hope this helps.
Regards,
Warren