I have the locking FOLD-A-COVER hard plastic folding panels that stacks up behind the truck window about three inches when folded back.

When I was towing the fifth wheel I also used a small marker tape on my rear window to align up with the center of the pin box. I had good vision using the rear mirror to align things up with.
My ultimate goal back when I towing the fifth wheel was to get setup something like this for my truck.

About all I got installed was just the front bed mounted 'personal caddy' tool box before I stopped towing the fifth wheel. This was a bit hard to gain access with the fifth wheel in tow and I had to use the slide back feature of the hitch to use it.

photos from google search
Now all I do is tow my OFF-ROAD POPUP trailer and my truck bed looks like this when on trips.

I really love my FOLD-A-COVER G4 ELITE and have moved it to two trucks since being purchased in 2008. Provides great lockable out-of-sight storage for all my goodies I can't live without on camping trips.. Everything under the folding panels is also protected from the weather elements.
Roy Ken