Sounds like time for a 'rethink' of this job. I definately like the idea of thinner slats on a stable substrate. I think I'll use 3/8 ply (unless I can find some core-cell), skinned with glass/epoxy, and then slats of teak epoxied to that (after the acetone wipe). Sounds like the black 5200 might be a better deal than the graphite/epoxy for the grooves. Time to tune up the band saw, install the wide blade (4 tpi), and make some 3" slats.