When we used our caravan in France this year - the first time it had been used after the winter - we found water leaking into the shower compartment and the vanity unit next door on the other side of the shower cubicle wall. OH traced the leak, and we found it was the shower valve itself. We'd drained the water out of the whole system before last winter, but apparently the innards of the shower are a '***' point where the water doesn't drain even though the valve and all the taps were left open. During the heavy frosts this winter the small amount of water remaining in the shower valve obviously expanded and cracked the plastic where the two water supply pipes join on. We had to repair or replace as we couldn't run the water system because of the leaks. The only way was to block the two plastic pipes which went to the valve, isolating the valve, but allowing the remaining taps to work. We couldn't find anything in the caravan of the correct diameter, but fortunately the campsite shop sold airbed bungs - and two of those, plus some tiny jubilee clips, did the job.
It was very awkward to do as the pipes run through a very small space where they needed bunging, so we were both needed - my much smaller fingers to hold the pipes and keep the bungs in place, and OH to tighten the jubilee clips! Goodness knows what anyone looking in would have thought if they'd seen OH lying on the floor and me straddled over the top of him!
A replacement shower valve is £92.00 from our local dealer, so sadly our caravan is now showerless. We've never used it in eleven years, so won't replace it until/if we decide to sell it.
I'm glad to hear that you got good service from your dealer - but we've generally found that caravan accessory shops, such as Narbonne Accessories which have lots of branches, are competively priced and carry the same range of spares and 'bits and bobs' as dealers do here.
We also did rather better than you with weather - we were away between the 20th May and the 13th June, and had a couple of half days of rain, a couple of dull days, but probably 18 days of sunshine! We never book sites and always follow the weather - and usually find the sun in the Languedoc area somewhere.