Our caravan which is the twin axle version of yours had a repair done for damp around the cassette door in July last year. They had not picked up the damp at a service several months previously and it is a known problem on 2011 caravans. Anyway in August the caravan sat in their workshop and was supposedly repaired.
In October the AWS checked the caravan and found damp readings in the same area of 20% which is only just acceptable although considering the repair it should have been lower.
About 3 weeks ago we discovered what looked like bubbling on the aluminium skin in the cassette area. Apparently this can happen when a staple inside on the wood rusts due to the damp and then reacts with the aluminium skin so you need to be careful. For peace of mind get in an AWS technician to do a damp test.
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