Hi Arch,
I've had one for about 10 years. I made it from a very cheap photographic light stand and a dark, opaque frisbee. The cheaper the light stand the better. Higher quality light stands are heavier and more robust than the cheap ones. You basically just want a lightweight aluminum rig that will fold up very compactly that you can toss in the car. The sections of my light stand slide up and down inside of a compression-type fitting that you finger tighten.

The standard thread for photo lights and tripods is 1/4-20. I cut a piece of 1" dowel about 2" long. One end will be CA'd to the inside of the frisbee. You'll need to rough up the frisbee with 80-grit where the dowel will be glued on and a fillet made from CA and baking soda around the edge of the glue joint will prevent it from breaking loose. Near the other end of the dowel, sand a flat spot on the side of the dowel and drill and tap it for 1/4-20.

I take the frisbee off when I'm done for the night so the glue joint won't be stressed during storage and transportation. I also slide a 5 pound barbell weight over the shaft of the stand which sits on the tripod part of the light stand when I set it up. That's where the compression fittings work better than a thumb bolt so the weight can slide down the shaft toward the tripod. There's nothing more disconcerting than having the wind blow the whole works into you while flying! The weight will make the assembly stay put in wind up to 15 mph or so.

Hope this helps!

Verne