I had Greg Meuller (from the Astro-Photo mailing list) manufacture a G-11 mounting platform for me a few years ago. I intended to use it to simultaneously mount a Vixen 4" refractor, a guidescope, and a widefield camera. I just don't have the time to go ahead with this project, so I'm selling the various components.
This platform is 18" wide x 22" long, with a standard Losmandy G-11 dovetail running the entire length. It's made from 1/2" thick aluminum. Don't know the weight but I'd guess at least 20 lbs.
$50 plus actual shipping charges.