We bought a new 31ss this last year and have not problems with it at all. With four grand kids and the dogs I would think that a 31 FS with the bunk beds would be the way to go.
The mileage is not great, we are better than most, we get over 9 mpg but keep it under 60 mph. If you are considering the greyhawk, the new model's cab over is all fiberglass one piece, unlike the cheaper competitor's model's seamed that can leak.
Jim and Sharon
Jayco 2011 Greyhawk SS31