truck topper
My first truck had a 'Roll N Lock' cover, so you'd just unlock it and roll it out of the way to tow. With my new truck, they no longer offered the metal one, and even if they did, it wouldn't allow my generator to fit under it anyway.
I finally found a custom made topper for 5th wheel use. It has a hatch over the hitch to tow with (comes with a rubber boot to seal the hole), and a hatch behind that to allow hitching/disconnecting. Also some other hatches to allow access to the bed for storage.
Unfortunately, my pin box was too big for the unit, so they made me a '1/3 bed' cover, which just covers the front 1/3 of the bed and leaves the hitch exposed. One hatch over the generator and a matching one on the other side for storage.