From what I have always heard, they used OSB for the floors in the slide. If yours is black, maybe you should check for water damage.
The floor dropping down on the end wall is usually caused by the slide being used when it's retracted. There isn't any support on the inner end when it's in the retracted position. Mainly because it raises up when it comes in and the leading edge is off the floor. I have made a set of boards I can slip under the edge when it's in. That way it's supported and we can use it when traveling and stop for lunch.
That was a big deal back when CR started building these rigs. Much talked about on the forum. Plus, a few end walls that got blowed out.
2008 Cruiser CF26RK
2013 Ford Eco-Boost
Heavy duty payload - Max tow