I have just finished cutting my final sled. I used 17mm form ply figuring that the black face will help reduce drag.
I had a little fun cutting the Maslow logos in the the front face! I think it looks great.
I have also designed and printed some chain guides that attach to the factory motor mounts with the factory screws. They seem to work really well! UPDATE: I added these red pins to not allow the chain to come off the wheel, they just push in to the cut out for the screw and are easily removed for calibration ect.