What is your recommended product for sealing funfoam?
I use different things depending on the use/effect I’m going for!
For pieces that will be somewhat rigid or stationary, I use Sculpt Or Coat. I really like the finish this gives, and it adds a bit of durability to the foam, but it’s flexible enough not to crack on drying like wood glue or gesso.
For pieces that need a smooth or gloss coating while retaining a great deal of flexibility, I would suggest FlexBond. I previously wrote a detailed tutorial/demo on FlexBond; it can be found here.
For pieces that require a flexible matte finish, I use acrylic spray sealer. This is easy to apply, and you can use more or fewer coats to achieve the finish appropriate to your project.