I've had a nem on the foam and not cause any damage to it. But I can see how the nem could easily push the foam cover off since they aren't exactly a tight fit on there.
The ones you saw were to buy or a homemade type thing? Would love to ditch the foam for something that is less flow restricting.
Someone on RC custom built them. I had the thread bookmarked, but lost it while cleaning up my bookmarks.
