hi ghost and welcome to the forums...
longer AND older become problematic when combined.
yes there are pre 70s units longer than 25 feet, but they are narrower too, and don't 'feel' very spacious inside.
and did not have 3 holding tanks, many gadgets or much carry capacity.
so making an oldie 'modern' or using a 50s or 60 longer trailer for LOTS of travel are issues...
here is a recent thread on this issue...
Whats the most desirable Airstream models and why?
and much more info on the topic from the other end of the looking glass...
Any Years or Models to Avoid?
Beatrice Years - Years and Models to Avoid?
Years to Avoid?
Pre-owned Airstreams - avoid which years?
Trailers to avoid
Airstreams, were there bad years??
so it seems this issue has come up a few times....
i would not want a LONG pipe frame trailer except for shows unless totally rebuilt....
same with the early rail frame units, frame beams are stronger now, but still NOT strong enough, as the weight crest 11k.
cheers
2air'