Now that hurts!!!
About the first thing to do is find out how the slide(s) are made from the manufacturer then go to work. I know my answer is pretty simplistic, but a slide floor repair job is that way. There is a top piece of plywood or in some cases, MDF or OSB, a piece of foam insulation then a bottom layer of 'something' which may be fiberglass, ABS or luan covered with 'something.
If I were to make that repair, after stripping the interior of the slide, would pull up and trash the carpet, it's moldy. My history with RV carpet is that it continues under the wall, is stapled with literally thousands of them and may also be glued. Once you get that carpet up, you may find that the damage is limited to one area. If so, carefully use a circular saw and cut only the damaged area out and only to the depth of the flooring. If it's the whole floor, again, remove it that way but in pieces. There is no magic formula to this repair - it's nasty and time consuming. Just covering black mold with new plywood will not make it go away. You will still have those mold spores along with the odor floating in the air.
As far as doing a floor repair - yep, I have done it but not a slide interior floor but the exterior cover though have done other interior floor section replacements. Not something I enjoy
A quick note - why not tell us what your TT brand is either in your signature or personal information.
Dave W along with my DW, Susan and our poodlepups, Callie & Molly,2011
Ford F250 6.7 CCLB, 5er Hitch Option w/B&W Hitch,,Ride Rite air bags, 2014
Montana High Country 343RL (38')