Welcome, and you are fortunate to have the opportunity to travel for a year with your son. He may not remember all the details, but he will remember the feel of various parts of the US, and will remember some things you didn't expect.. (Weather, or scary things or smells...)
As a first timer going for a year, buying new might be tempting, but I'll put in pitch for gently used, say within 5 years... Less depreciation and more likely the little bugs have been fixed by prior owner (PO..) rathern than leaving you with the task of handling under warranty...
You didn't mention towing vehicle, but at those lengths and weights, a 3/4 ton crew cab or Suburban are going to be required. Due to fuel price increases, some of them are also available at substantial savings over brand new with low mileage and good condition...
In your area, Colonial RV in New Jersey is a large volume dealer, with a few trade-in's. The other major sources of leads for used trailers are:
1. The classifieds here on the Forums above..
2. Vintage Airstream Club classifieds (The Vintage Airstream Club
3. RVtraderonline.com (search for travel trailer and Airstream brand)
The Airstream.com website is a good source if you are committed to finding a new trailer, as many dealers post their inventory their for a regional or national search.
As cool as the slide-outs look, they do add weight and complexity and possible maintenance chalenges, and any of the units with a dinette would work for meals and reading, etc.
Cold weather advice above is good.. Driving in snow or ice is a real challenge and to be avoided if at all possible. The trailer will work fine when parked in the cold, and the interior furnace will keep water lines and tanks from freezing..
p.s. A great tip for posting new messages is to use "Edit" "Copy" feature before hitting submit button, so that if computer server doesn't respond, you can avoid retyping the entire message and just paste it in again...