So someone named Chris (assumed spelling, and I don’t know your @ so I hope you see this!) asked about 3D printing a clear gauge cover. One possible solution I thought up would be to 3D print the piece, make it as smooth as necessary, then make a silicone rubber mold of the piece, then cast it using an appropriate resin. However, the easier solution is probably what someone else suggested: 3D printing the part that clips into place and attaching that to a clear plastic cut to shape.
P.S. If you happen to see this, I would in fact like those spare Wii top covers for the gamecube ports you offered me yesterday, because the filament I bought is very uncooperative.