Selecting a 5th wheel hitch for my truck/toy hauler combo

Got the hitch put together and installed last night. Pretty straight forward. The only thing that seemed cheesy was the spring mechanism to keep the head tilted back when unhitched. I have no idea how this thing is supposed to work properly, it doesn't seem to do much at all.

One thing I hadn't thought of was, can I use a toolbox across the top of the bed rails with my longbox?

I guess I'll find out when I pick up the trailer, but I was hoping to be able to keep all my usual "truck stuff" in the box when towing.