if you could would you use it , if all you had to do was to shape the rails and cut in boxes , you think it would be to stiff even if you dont use a center stringer at 1.5" thick ??
I've used it on the rails only and it's really stiff. Stringerless EPS is 2+ pound. I think you could use it without a stringer with an adequate glassing schedule.
i might try 3lb. at 1" thick on a shortend version of the xbc fish, make it 4.8 with a flat bottom with 2.5 nose and .5 tail rocker and install a quad fins