If I needed to seal specific areas, I'd decant some plastikote T-235 to a jar and use the airbrush to keep from burying the rest of the project. Kinda treat it like drywall compound, start in the middle then feather out farther. Airbrush will keep it localized, just work the areas that need it.

A good general sealer for multiple surfaces is B-I-N, in the regular can (pretty much a lifetime supply) just have the hardware store shake it real well. Thins with shellac thinner (denatured alcohol) but be sure to strain the thinned mixture into your airbrush jar.