Perhaps a creative solution. How about a coffee table or trunk. I piece of plywood for the width and foam rubber on top. The truck or coffee table would be useful during the day. The piece of plywood should store under the bed. Finding a place to store the foam may take some thought, depending on the coach. I would think this would go at the foot of the bed, so there really would not be much actual weight on it.
At least those are my thoughts, and I have the same situation, but right now, I am going with "Sorry, our coach only sleeps two".
2008 Monaco Camelot 42 DSQ