Hello Siobhan,
First of all welcome to the forum. I'm sure you will find many like minded people here to share problems and anecdotes.
Its a real shame to read of your current difficulties, and having carefully read your post I'm not convinced your problem is water ingress - which is good news.
The presence of moisture around the shower tray and its absence on other wall areas is most likely due to a sealing problem or a leaky pipe around the shower rather than a wall or roof seal leak.
Unfortunately, regardless of how the problem has arisen or who may be responsible, its going to take some time to put it right, so you are going to have to factor in this time to your arrangements.
The following notes only apply if the fault has become apparent and not caused by improper use or accident.
In theory you have two possible ways to proceed. The first and probably the simplest way is to use the manufacturers guarantee. You must abide by the terms and conditions you have with your guarantee, which will entail you having to take the caravan to which ever repair shop is approved to undertake the work. Unfortunately if you use the manufacturers guarantee you are not able to claim costs for delivery to and from the repair shop, nor automatic compensation for loss of use.
The second method is less certain. When ever you make a retail purchase you are automatically covered by the Sale of Goods Acts. This in essence requires the seller to only supply perfect fault free goods, that are durable. If a seller sells faulty goods then they are legally obliged to remedy the situation with the minimum of inconvenience and cost to the customer. This could include a loan caravan for the duration of the repairs.
Now in your case I suspect its not quite as cut and dried. If the fault became apparent and was reported to the seller within six months of the date of purchase, the law will tell the seller they must remedy the situation. But after six months it is the responsibility of the customer to prove the cause must have been present AT THE POINT OF SALE. Your caravan is more than 6 months old, and I suspect you would have considerable difficulty in demonstrating the age of the fault to be precede or be close to the point of sale.
I suggest before gunning for dealer or manufacture, take a deep breath, and actually talk to your dealer avoid becoming confrontational, and ask if they can help, you never know it might be better than you think.