Actually the problem was with the older Polybutylene gray stuff.
There is an ongoing class action suit for stick built and mobile home applications.
Apparently long term exposure to hard water cause the fittings to breakdown.
The newer, and current QWest Pex white or color keyed stuff is supposed
to be the right stuff. For a manufacturer like Airstream which has been
committed to crimp fittings for many years it was easiest to stay with
the metal crimp fittings. Some other well regarded manufacturers did change
over to Flair-it. Although Flair-it had to be altered slightly to allow
for Pex slightly different dimensions.
Our recommended choice for ease of use it Flair-it with Pex line. No
special tools are required and it is much easier to work with in tight
spaces.
Charlie