When I was in the service I moved without my family once and spent 5 months in my 24', single slide.
I agree with most of the people here....
A slide is a must
A recliner is a must (pull out your cheap couch and put in a chair if you have to)
A fixed dining table
and A ROOMY SHOWER. (I think the small, camper shower was my biggest complaint the whole time.)
Anyway, I would like more room and storage if I was full timing than my 24 footer gave me, I've got a 32' now and I think it would be almost too big if I was alone... so yeah, right near 30 sounds like a nice round number solo.