Lunar Quasar 494 - 2012 - Damp Problems

Purchased van new Feb 2012 & on its 1st service March last some damp found in area of toilet casette area.This was supposedly put right after fitting new exterior door for casette/fully sealed etc.Just heard from Approved workshop that this yrs service has revealed extensive high damp reading in various parts of van which prima facie ha sresulted from condensation rather than ingress.So what to do ? The problem is apparently becoming commonplace which begs the question - is there some fundamental flaw in materials /design.I recall extensive dmp /condensation in vans in 1970's but surely we have moved fwd.? I am asked now to return van to wkshp in 10 wks time to re check levels when hopefully they wil have a solution after liasing with Lunar.Anyone else sufferring similar grief??