We have a 2000 Eagle with a couch like that and the people who've slept on it find it really comfortable. While Frank has never "slept" on it he sure has enjoyed some fine naps on it. He is 6 feet tall so to spend the night on it might be tough but shorter people have used it and have been very comfortable. Definitely isn't big enough for 2 adults but possibly one adult and a small child.
I'm sure you will love your Designer, they are my personal favorites.
Kay from CNY
Frank & Kay, Central New York, 2002 F250 PSD, 2000 Jayco Eagle 266