I have never airbrushed Future, and I see no reason to take the time to do that.  I apply it where I intend to decal with a Q-tip, and then throw it away, i.e. no clean-up time or trouble.

That stuff is so thin when dry that you can make a wet puddle with it on a flat surface, and it will be totally smooth with no discernible thickness when dry.
Marvelous stuff.

It can be dissolved and removed with household ammonia, if needed.

Dick Harley