Masking, any way you can

Masking can be done with masking tape, liquid mask, paper, stencils, or anything you happen to have lying around and you find handy to use. As long as it does the job of preventing paint to come in certain spots, you're doing it right.

A plastic bag is actually a lot easier to handle than a sheet of paper.

Making sure the plastic won't stretch or tear around the diving planes.

The Puma's interior is protected by a paper disc, secured in place with latex.