We have a 2012 back country 18f which is 22 feet. We now have two kids one is 5 the other is 2 months. We are looking at trading ours in but it seems the only size that will work is 33 feet with bunks...
As our girls got older they finally decided that tents were more fun then listening to mom snore. We used a 22 footer for years just fine. Once they went to tents we upgraded to a 30 footer and hated it with a passion. Lost too many nice camp sites to the large trailer. I would say don't do it.