Iím not sure itís fair to blame the dog crate for that much floor damageÖmaybe part of it. The bottom slide trim angle was probably leaking for a long time, maybe even the window above. Since your RV is permanently stationed under roof now - the leaks donít matter. Iím not sure how to find and kill all the mold.
James the AZ RV Expert on YouTube has a video where he replaces a bedroom slide floor in an older Montana - but you can see how he addresses the leaky spots.
MikenDebbie Aggie Ď77 in the sticks near Austin TX
2019 Chevy 3500 High Country DRW
2018 Montana 3921FB
Aussie Gus + Texas Heeler Jimmy