Deano,
Future doesn't seem to have any affect at all on Mare Metal Foil - the shine is still as good as it is with no future coat. I've done many leading edges on airliners and then clearcoated them with Future with no ill effects.
If you're doing it on a car, it might be easier to clear coat it first and then put foil on it.
I always apply Future with an airbrush (or a dip for canopies).
Cheers,
Lee Tree