For those of us that do not have the resources: use Elmer's glue. You can thin it with water and paint it right onto the foam.
Do you have ratio of glue to water you can recommend for this?
Mod Podge will do this without thinning - it's a glue and sealer that dries clear and is nice and liquidy (sort of like 2-3 parts glue to 1 part water or so; not so thin it disappears, but not quite as thick as white glue alone)