Personally, I would never use an adapter on a heavy trailer. The adapter acts like a lever, and will flex the trailer frame where it Z's up to the 5th wheel pin area. The frame will eventually crack and break on a heavy trailer. Use a B&W Turnover Ball hitch under the truck bed, and a B&W Companion Hitch in the bed to tow the 5th wheel. The companion attaches to the Turnover Ball hitch, and there are no rails in your truck bed to be in the way when you aren't using the 5th wheel Companion Hitch.