I have a 2015 Windsport 27K as well, and I know about the canvas bag you are describing. It wasn't there because of a leak; actually it is meant to guard against abrasion of the wires and tubing against the floor when the slideout moves.
But, in your case it does sound like it helped to contain the leak.
By the way, on my 27K I moved the electrical box in that same location so it was out of the way. The original installation had it so that the cables were rubbing against it when the slideout moves.
Hope you find the source of the leak.
Tom
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