I haven't had any issues with too much water, actually mine dry very fast and I use a fan on it when done to speed it up even more. The OSB used in mine at least, is the Weyerhauser structure wood, rated for exterior use with a 25 year warranty. Not at all the same stuff as particle board. I had a leak 3 1/2 years ago in the back of the trailer and have seen zero signs of any wood or glue failure. The carpet pad on these is pretty minimal at best, so doubt it holds a lot of water. If your carpets are actually wet when done, your machine isn't working right.
PS; I have particle board underlayment on my floors at home and have had them steam cleaned for 25 years, both with a home and commercial service. When we ripped the carpet out of the living room a few months ago, there was absolutely no indication of any water damage on the particle board.