We bought an S1 Valencia 2 years ago from a well known dealer. The damp report said the floor was perfect and rot free, but when we went away in it a week after purchasing I nearly fell through the bathroom floor. The dealer was very rude about the issue on the phone and very reluctantly booked it on for assessment - we then watched the service manager go over the floor and he said the damp readings were so high and the rot so bad that the caravan was beyond economical repair. They swapped it for a 2 year newer S2 Valencia at no extra cost and, to keep us quiet, included a 5 year warranty. The S2 has now been back 3 times for damp repairs - the front locker floor has been cut out and replaced, a section behind the off side wheel arch has been cut out and replaced, and the floor under the bed and bathroom has had to be dried out when the under bed locker door warped and leaked. We still have 3 years of warranty to go otherwise I would be selling and buying a different make - but then are any of them any better?
If you buy a van ignore the damp report they give you with the PDI and check yourself or get someone else to check (a mobile caravan repair company perhaps), and keep an eye on it. The only part of a Unicorn that rots id the floor.