A soft wire brush in an angle grinder is very effective at both removing foam and turning you into the abominable snowman at the same time. I recommend doing that outside...
Why not cover the foam cores in perforated plastic (or just thin tape with some exposed foam around the ends of the panels). That way you can just rip the foam out after all the skins are made. Obviously, you need a temporary stiffener on the outside. Some local peelply you laminate on the outside with some wrapped foam stringers on the outside skin? Pretty easy to remove but until it is, pretty stiff. And no risk of damage to your skins when you remove the supports.
Kennis vermenigvuldig je door het te delen.
(You multiply knowledge by dividing it)