I've played around and exprerimented with using just wood as a sliding surface and i'll tell you... i would steer clear of that for sure. It sort of slides mehh when it's dry, but as it gets damp it's like hitting a sticky rail.
With water constantly drying on it you have to think about the wood swelling, contourting, and bowing over time. And i would imagine edging into it would be a mess, although i haven't tried that. I Suppose if the wood box was always left in freezing temps outdoors with a nice thin layer of ice on top it might work. But then with that... there would eventually be lumps and shit all over it.
My advise... stick with cheap pvc or spring for some HDPE. General rule of thumb... "anything you can sink your fingernail into and leave a mark would not be a good sliding surface."