I just purchased a used trailer from a dealer and discovered soon after getting it home that the floor in the bedroom slide was rotten. Keep in mind with a bedroom slide (at least mine) that the floor on the inside of the unit is not the same as the lower portion of the slide you see from the outside. Mine has two floors separated by the aluminum square tubing that makes up the slide framework. I was lucky, I put up a big enough stink with the dealer that I bought it from that they replaced the rotten bottom wood of the slide for free. I have read a lot on this subject and it seems the most common cause of rotting floors in slides is water wicking into the wood from trim screws.
There are some interesting videos on YouTube about replacing slide out floors. Some people do it without removing the slide from the unit. Others remove the entire slide to replace the floor. I was ready to do mine myself if my dealer had not offered to do so.