I haven't tried it that way. Did you just buy the gun? See if you can return it and get an iron instead.

Someone else might chime in here, but I'd be concerned that the gun won't get the cover to adhere correctly to the balsa on the fuselage and you'll end up with bubbling and inadequate adhesion.

You might want to give iot a try on some scrap pieces, though.

BobbyG