I had the same situation with a nice rotating ball in my truck bed
Look up the STAR Performance Kingpin Adapter (Gooseneck adapter).
Have towed my 13K Fiver since late 07 successfully with it. It includes a glider motion that attenuates most likely encountered stresses and eliminates chucking except under the roughest conditions (slow down to stop it).
Very rarely have we been in a Campground without at least one other fiver with a lesser sophisticated gooseneck adapter.
Keeps the truck bed free, never have to worry about dropping the trailer, gentler raising and lowering hookups, but is slower contingent on the speed of your jacks.
