-- Last Updated: Oct-27-12 11:05 AM EST --
I'm not especially crazy about the rails being screwed through the outwales full length.
There are also a couple of details in the third photo that might make me agree with papav. Way to the left it looks like there might be a tank, and that funny shadow in the middle could be the edge of the core.
FWIW, I would have said Royalex at first glance.