Not sure of your snow load , but if you have a large Ice & snow load on the roof you could be causing bowing of the unit(snow & ice can add 20 pounds per square ft to the roof) and it would cause the seals to twist just enough to cause a leak....also check your vent area for Ice-over this causes ice dams and water will walk up the seam into the coach........it is very important to cover or tarp roofs in the north for these reasons.

-- Edited by Lucky Mike on Monday 25th of February 2013 08:24:45 AM

If the slides were in tight while stored, I would not expect that they were leaking. You might check the seal around the back window as that could be leaking. The water may run down the inside of the wall and wet the carpet at the back of the unit. You might also check the seals around the lights in the back and also the seal where the rubber roof meets the fiberglass rear cap. Any of those places can leak and allow water inside the wall where it can travel down and find its way inside the trailer at the base of the back wall.
Depending on how long the water has been on the floor, you may want to have a dealer check the floor and make sure that the plywood has not been damaged where it would begin to separate or rot out.

We had two leaks in our first year at the rear of the large slider of our Montana. The first was noticed after I washed the top of the slider and both sides of the slider awning. We had water inside our cabinets. The tape that runs along the top of the slider had started to lift at the edge just before it runs down the side wall to the trim.

Our other leak was noticed by wet carpet and this turned out to be the window at the rear side wall of the slider requiring re sealing.

Good luck!