Hello John.
Its good to hear a positive comment about a manufacturer especially on teh matter of water ingress.
There will be other members who I am sure can report that thier UK caravan has not had a problem for the same number of years, but as they say a Swallow does not make a summer,
The problem is not that UK caravan makers can't design a leak proof caravan, they just can't or won't make them consistently.
I'm pretty certain that if you were able to survey Fednt owners some of them will also report some damp issues, whether the proportions of failure to good would be the same I don't know, so your failth in the marque may be justified.