I’d also use it for fishing poles. Id put a little piece of paracord at the back of the camper to hang the butt sections from the roof and then put the tip sections through the camper into the cab of the truck!
Seems to me like it would useful for providing airflow when transporting your furry friends.
I could also see someone creating some kind of insert and duct setup with a flat hose to get heat (or A/C) into the downstairs without needing to cut a hole into a side panel. Might be challenging to install, but would maintain the panel warranties and minimize additional orifices through which someone might try to break into the truck bed.
I would use it to teleport cold beers.
The dog likes to check up on us frequently. We have a regular cab, and we would likely bring the dog along on our cross country trips with the truck/camper access. Access could be handy in inclement weather. With a small passenger compartment, anything the gal pal can access while I’m driving would be a major time saver for sure.