I too have an F350 with the 5th Wheel/Gooseneck prep. Ford partnered with Reese for the prep hardware. We also just acquired a new 2015 Pinnacle 38FLFS which is a bit heavier than yours dry, but understand your concern. I almost settled on Reese's slider ($2,100) that drops into my prep since I have a short bed.
I didn't want to lug a 150lb+ system in and out of my truck and I'm not a fan of the bucking and chucking a typical 5th wheel hitch offers.
After months of research, I have settled on the Andersen Hitches Ultimate 5th Wheel Connection. Check out the video on this page:
http://www.andersenhitches.com/Catalog/ultimate-5th-wheel-connection.aspx
After discussing the solution with my dealer, without knowing it I found it is his preferred solution as well and he has been using it for quite some time with his RAM pickup. I also know the Ford Louisville Plant Vehicle Engineers and shared this with them. They see no issues with the Andersen solution from the tow vehicle side.
You'll find the Andersen Ultimate 5th Wheel Connection is rated to handle more weight than a typical 5th wheel hitch, is lighter in weight (75lbs), is 25% the cost, and doesn't have all the chucking and bucking you get with a typical hitch. :)
Be mindful that if you choose not to use a typical 5th Wheel hitch, Lippert who manufactures the bulk of the 5th wheel frames for the industry, may not honor their warranty. I've been told by my dealer that Andersen has prepared for this and will honor any warrantied damage that Lippert will not.
Looking forward to what solution you decide on.