With a basement model Lance, I don't have access there when the camper is on. Period.
What I do store there are items I need for the pickup bed when I remove the camper while traveling. I have a 2x6 hinged in the center that folds in half. Unfolded, it spans the truck bed to help keep cargo from sliding toward the rear. The ends are contoured to fit the corresponding slots in the edges of the truck bed. It fits very tightly when installed. I suppose I could provide a photo if someone is really interested.
I also have a rear tailgate net thingy (Bully brand) that keeps cargo in and satisfies certain state's laws requiring a tailgate.
2019 F-350 4WD Crew Cab DRW 6.2 l gas engine (6500 lbs cargo capacity!)
2007 LanceMax 1181 loaded, King memory foam mattress (driver's side locker omitted).
"Leave the trail a little better than you found it."