I have had my SG and GPS in various locations in my car.
While this setup worked because I am left-handed, My eyes were having to shift all over to get the various readings.
If you are 'using' your SG like I do, you realize that it needs to be at the same eyesight as the other gauges in the car. It also has to be mounted securely so you can tough the buttons to change gauges.
I finally have decided to mount the GPS and SG right in the middle.
About 4 years ago I had a black acrylic shield made to reduce some of the glare on the center screen. You can see it in this picture.
While I liked having the GPS and SG right there, when I would look at them I would get the light from the uotside and it was tough adjusting. I drive 6-10 hours at a time on some trips and I needed to do something.
This week I finished a cover.
I used a plastic nootbook that had a grainy surface on it.
I built the shape uot of thick poster board, the glued the plastic to that. My experiense has been that plastic will lose it's shape in the heat inside a car. The thick poster board helps resolve that.
the edges are trimmed with door edge trim that is available at the auto parts store.
I didn't use any glue to attach it. I wegde the back edge into the trip along the dash. THe the piece near the steering wheel is folded and wedged into the dash trim.
I used this setup on a drive to LA last week. It was much more comfortable on the eyes have the dark shield arounf the GPS