We had a Cougar for over 10 years:
We started out pulling it with an F-250 with a V-10, and ended up using an F-350 with a V-10 (as you see in the image above). The combination weighed in at around 16,000 lbs total. Primarily moved to the F-350 because the tongue weight of the 5th wheel was close to the max payload on the F-250.
We liked the Cougar a lot, but wanted something a bit smaller (hence the move to the Axis motorhome).
The dry weight of our Cougar was around 8,000 lbs thus the one you're looking at is likely 2,000-3,000 lbs heavier than ours. I'd highly recommend at least a 3500 pickup to pull that around.
With 5th wheels you really have to watch the hitch weight. Typically the hitch weight + the trucks weight will easily exceed the GVWR of a 2500 series truck.
Keystone has changed hands a few times since our camper. The new ones I've been in have looked really nice.