Before I could offer a suggestion, I would ask whether or not you have a short box or long box. Next, I would ask, at full travel across the arc of the nose cap of the trailer, how much room is there for an extension?
I've seen cab extensions, similar to a topper, that mate up to the rear window for a small sleeper area. They go back from the cab about 2 feet. I did some research on the web but couldn't come up with anything specific. Leer, ARE and Gem Top are manufacturers that come to mind.
2006 Chevrolet Silverado 3500
Crew Cab, Banks Power