I’ve seen this mentioned a few times in the past:
http://www.industrialpolymers.com/styrospray.html
and was wondering if, for example, you could take low-density EPS (1-1.5lb), put on balsa rails, seal the EPS with a brush-on version of Styrospray for added strength/ding resistance, and finish it with a light glassing schedule and epoxy. I was trying to come up with a simple way to build a rail stringer board with durability and flex in mind. Based on the elongation numbers on the website for most of the coatings, the “shell” shouldn’t be the flex-limiting factor. Any thoughts?