Welcome to the club!
I had seen your camper on eBay. How's the roof look? I thought I remembered the seller had replaced/repaired it? It's possible he already stopped the water infiltration but you should carefully inspect all seams for voids in the seal. Not just the roof, but everywhere. Also check for plumbing for leaks.
Hope the damage isn't too bad and your certainly not the first to experience this.
There's a custom Google search for this forum that works pretty well......
www.cse.google.com
Good luck
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