Not that thin, but I have made boards with 3mm ply top and bottom and foam/wood in the core. Hold up well, chop eaters, but not enough pop.
Anyway, rails are a couple layers thin birch plywood, glued with epoxy mix thickened with cotton flock and a bit 'o colloidal silica, shaped with sandpaper and rasp, then another coat of epoxy to seal.
Kinda primitive, I know... wood is tough though. Tough is a good property too
Surprisingly, not seeing any rot in the wood after a couple years and a bunch of scrapes. I guess it dries out fast enough to avoid rot. ABS would be as easy to shape, but more work to bond and repair. ABS seems a popular rail material, but a bunch of folke have done rails out of urethane compounds they mix up and pour like epoxy. These might be the best, given urethanes physical properties - strong, good bond, flexible.... Someone posted a pic recently in this forum of one with wood strip core and green rails and fin blocks (urethane?) under clear glass. ...looked cool.