Spongy flooring in slide outs

thanks so much! We fully intend to get rid of the mold and to find out where the initial problem lies. We bought the whole kitten caboodle from my inlaws, and he says that at 'one point' there was a water issue but it's since been resolved. I just think that since they didn't take it one step further to see what may have been damaged, it's gotten to the point where it has to be replaced.

Still open and welcoming to more ideas, suggestions and advice!