Had this leaking when my top slide seal was not sealing correctly. The water would run along the roof of the slide, down the side and onto the ground. I had the same pool and flow along the floor and to the rear bathroom area.
Depending on how hard it was raining, mine at least, did not have a slide topper so what is on the 10 x 3 slide will need to go somewhere when it is retracted.
That being said I also get a bit of a puddle when I retract in the rain but it does go away since it is only what was on the roof.
Pat, Jen & Heather... Oh yeah and our trained attack trailer cat, Cinnamon
2015 ChevyHD D-Max
2014 Greywolf 26DBH