i will piggy back tail gunner a bit
if you want to stay in a towable ( non fiver)
they go up to 40 feet. yep
$$$ is you only limiting factor.
i would say go see as many brands and styles as possible,
and get a feeel for what suits your family or camping intentions, (r v parks, primitive, desert, etc) then decide how many folks need to be comfortable inside and sleeping, plus plan on a real bad day of weather and think "cabin fever" then if its bog enough or comfortable , you have found your floorplan.
then go compare floorplans of many brands and pick em aprt for quality and fit and finish, etc
if it has slides, ask yourself if its important to be able to get to the toilet without opening a slide, many new ones now for some reason close off everything but the kitchen sink when all closed up. when we are on the road, i prefer to use MY potty vice the rest area or stre, etc. so haviing access is a priority.
shoot some even block off the fridge which kills a quick snack.
and last but not least
cargo carrying capactity
many seem to feel they can give you only a few hundred real world pounds of cargo once you add full water and prpane.
if your only going to do short runs then 1k lbs capactiy might get you by ok.
it really does add up, overloading a rv axle is serious business, they just dont handle much over the rating before tires and shackles give way, and usually at highway speeds
we added over 3k lbs before one drop of water was loaded on.
look real close at axle load ratings and gross vehicle weights for the trailer.
you will be surprised.
good luck on your quest
rving is a great way to get back some family time