Toolman,
Not sure if I'm reading your post right, but it would seem that your interested in a gooseneck hitch which is mounted under the bed with the ball coiming up thought the bed. You would have to use a gooseneck adapter for the 5th wheel to work. A word of caution if you have a 5'er under warrantty. Most frame manufacters will void there warranty if you use a goosenck adapter. Here is what I have, a B&W turnoverball hitch. I purchased the B&W compainion 5th wheel hitch to go with it. I can remove my hitch and you can't even tell that I had one. Do a search for "B&W hitches" to find there web site. It will show you a dealer that is close to you
Coolbreeze1