(Note: you’re working with hot tools. Make sure to turn them off after use. And wear protective clothing such as heat-resistant gloves and possibly respirators.)
Sealing and shaping.
With a heatgun, you can give your foam a nice curve if needed.
Do this by briefly heating the foam with a fanning motion. Then immediately shape it into the desired shape.
For painting, it’s helpful to seal your foam before gluing. This prevents the paint from being absorbed by the foam. Do this before gluing, otherwise the heat will cause the adhesive to loosen. With a soldering iron, you can neatly burn through any small holes in your foam. Or for decorative lines.