Hello Surfer,
AS Dusty implies, caravans sold in the UK should be expected to withstand the normal yearly weather conditions experienced in the UK for the predicted life of the product.
If the manufacturer wanted to limit their liability in this respect, they should issue some kind of warning WHEN THE CARAVAN IS PURCHASED, and offer some strategy to manage the possibility. Incidentally if they did suggest for example that seals needed to be replaced annually, then they would be laying themselves open to claims of faulty design.
Historically there is plenty of evidence of caravans surviving all seasons in the UK so the generic design is fit for purpose, but if a particular caravan failed in the manner you describe, it would be exceptional rather than the norm and consequently self demonstrates either faulty workmanship or faulty materials.
We know from many threads both here and on on other forums/magazines, that there are a significant number of caravanners who have suffered water ingress problems of one sort or another, whether any have suffered in the way you describe is not clear, so whilst your query ,may by hypothetical, it may be fact for some.