I also live in Wisconsin and have had the same thing happen to my bedroom slide (April of 2015). I made a jig to go around the slide so that I can jack the whole slide up off the bottom weather trim. Bought a 4'x8' sheet of ABS plastic from Midland Plastic for $23, but after pulling the broken bottom off I found the front corner of the floor is rotten. The whole bottom has signs of black mold and is not solid enough to hold screws. Amazing that there was no signs of water damage just last year.
I posted a topic about factory fixing this vs dealer. I don't know what to do next.