I have had similar leaking in the past, though in the front of the unit because I park it with a slight tilt forward. You should let your dealer work this, since it may involve replacing some carpet or panels to make it like new.
I believe that the thing that will fix the leaks is a better seam (caulk) on the inside of the pan, where the sides are "lipped" and the joint is welded (but not waterproofed I suspect). I think that if those welds are caulked, any water that gets past the rubber seal will just be diverted back outside. To be honest, I haven't looked at the rear seal, to see if there is another avenue for the water to intrude into the coach. These are obviously engineering problems that the manufacturer hasn't corrected (since my unit is a 2002).