I suppose you don't care about any type of graphics on the bottom? Lexan Plexiglass is highly sensitive to impact strong scratches and marrs extremely easily. the thicker you go the better think ICE HOCKEY those are pushing 1.5" to 2" and need a crane to lift them. Not really a weight reducer
Another thing I've seen in the industry lately is these lexan fins. TOTAL GARBAGE do not even think about them they are terrible broke first time out. G10 glass is great lexan can't stand up to the side pressures exerted.
Last thought for your idea of hitting rails and such is UHMW It doesn't wear ever with metal contact its so soft but yet hard and doesnt deform at all. I think the snowboard bases are made with a derivative of this material and is sold in sheets that can be molded and cut with ease.
Delrin is another option but i'm unaware if sold in sheets its typically used for high wearing conveyors that transport items such as beer bottles and other high speed production conveyors.
Lexan needs an acrylic bond that melts and fuses it together. Unaware if it sticks to other materials but superglue is excellent for fusing the materials together there are some other industrial adhesives that are similar.
I think you're on to something great bringing the technologies of snowboarding and traditional water board building.