I would recommend you take a look at Hybrids. You get the tent camping feel with a full trailer with all the features. You get far more usable space when open than you have when towing. For example mine is 21' closed but when opened it adds about 5 additional feet on each end with 2 queen beds (effectively giving me a 31' at under 3500lbs). They generally tend to be some of the lighter trailers (especially for the volume you are getting). You can also get some models that have 3 tent ends (front, back and one side). With a jackknife sofa or dinette that converts to a bed (which are common) and you have lots of room for a big/young family. There are lots of HTT's in the 3500-6000 lbs range. Due to your weight budget, as tempting as a slide out may be for additional space, the frame/track for a slide adds a lot of weight. I would definitely look at WD, it improves handling quite a bit for me. I would also get a sway bar, nothing more nerve wracking than seeing some of the idiots on the road with their trailer fishtailing down the highway. Also I would look at getting a tranny cooler.
