the clearance area is 44 x 77 inches and 3 inches high. the side walls control that when they are in the down mode. we just used some 3" camper pad foam from our local fred meyer store . it trims great with a metal hack saw. we do sometimes ad an extra 1" pad of memory foam to the top after camper is raised. the foam pads makes it easy to put in and take out as we don't camp as often as we'd like to. in this moist climate, we usually keep pads and seat cushions in the house to cut down on mildew and keep them smelling fresh between trips and during winter storage. ours is a '75 -10' co
wes