I've had HDPE (Starboard), G10, PT, and plywood. HDPE is a hard NO for me. It will work, yes, you could counterbore the holes, and it will cost a bunch to not work better. Plywood works in some applications, but it;'s not what yours was designed for. G10 is a pretty funny suggestion. Heavy too. Just make it out of PT deck boards or what ever fits and figure on replacing it every 10 years ... if you still own the boat. The motor will be more secure. If there is a bracket where you can sink a screw into the boards, all the better.
But nothing slippery. No point. The mount you have was designed for wood.
But nothing slippery. No point. The mount you have was designed for wood.