We're run into singles in Scamps and Truck Campers a little to tight for me much less for two but our fifthwheel interior is 33 1/2 ft from the front of the closet to the rear window 35 ft overall, we do have 3 slides, and we've been fine fulltiming in it for 6 years.
We try to stay in state of federal campgrounds when possible and have always found a site, we seldom use reservations, though I do check availability on reserve america like the night before. I figure if there are sites many unreserved we'll get one if we stop early which we normally do by 3:00 pm.