I promised Brian that I would post pictures of my DIY Tether Tray...
I had most of the materials for this tray lying around. The only component I had to purchase was the 1/4 x 20 screw insert which will accept a standard tripod screw. That cost me sixty-seven cents!
The flat board, which is the major component, came from a store that was going out of business. It was display shelving and I was able to get several pieces of it. It is nicely finished and 11x21 inches. However any size that could accommodate your notebook computer would work.
The bottom edge of the tray is made from some old 1/8 inch aluminum "L" stock which I had laying around. But, anything, even a piece of wood, that would prevent the notebook from sliding off would suffice.
I attached the aluminum with two screws.
The shelving that I used was made of pressed fiber and would not hold the screw insert very well, so I glued and screwed on a piece of pine which could accept the insert.
The screw insert allows me to attach the tray and detach it without harming the structure. I drilled a 3/8 inch hole in the pine and screwed in the insert with a screwdriver. No hi-tech tools required.
I have mounted this tether tray on a 30+ year old Davis and Sanford tripod. This tripod is made of steel and can support a Volkswagen. Of course, it is as heavy as a Volkswagen also. Any reasonably sturdy tripod would suffice...