Assuming the previous owner did not do so, "right away" you will want to seal the 3 amber colored front-facing lights at the top of the cab-over bed, and the one on each side. They are prone to leaking in significant amounts of rain water and snow melt, destroying the cab-over area. By the time the owner sees water stains, lots of damage is already done. Also inspect the seam-work in the same area for the same concerns.
At 23.5 feet bumper to bumper, the 21QB is a sweet little rig with an efficient floor plan. I hope you enjoy it. It's the same floor plan as our rig minus the cab-over bed. Our rig is a B+, working perfectly for my wife and me 12 years running.