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Likely an idler pulley bearing, or simply an old/dry belt.
I think bags are my best option as the camper won't be on the truck 24/7 and will be an around-town vehicle when we are home.
I used Firestone Ride-Rite air bags on my 2008 Superduty and was very happy with them. Even with the air bag, the 2008 stock leaf pack sagged too much and I had to add couple of leafs to gain an inch height. 2008 was the first year with longer springs so hopefully your year has improved springs. Years earlier I had Air Lift brand air bags on an F150 and they were fine although I lost an air line connection on rough road once. Since I have the camper on the Superduty full-time I ditched the helpers and went with custom rear leaf packs from local spring shop and wish I had done this at the beginning.

You should have 4 inside hatch areas to put the turnbuckles in through, so you can tighten them. I know my old Grandby, one of them was access under the bench.

Wow, new and unused for 7 years. That is crazy. Congrats on the new camper.