Airstreams certainly have a nice upscale look and feel to them. The lower and narrower Airstream will tow more easily, too. (Although I'd hate having to slide around that table for every meal; the Lance dinette seems more sensible to me.) But like others have pointed out, your ready-to-travel weight is likely to be 4500-4800 lb with quite possibly 550-650 lb hitch weight.
Definitely look at the Escape, sold from its factory in Chilliwack BC. The 21' Escape is just a bit over 3000 lb dry. Its molded fiberglass construction will be unaffected by sea salt, and the lack of seams means there are less places to eventually leak. Escape has a good reputation for quality and their trailers hold phenomenal resale value.