Storage Bay Floor replacement

[lesmadding]

Hello everyone, I am fairly new to this group and being a Montana owner. We purchased a 2011 290RLT in March of this year. IMO its a very nice trailer, one that was well cared for and thus the reason we purchased it. However, I have discovered there is water damage in the crossover storage bay with mold and rotten flooring which I am in the process of removing now. This could be the reason the people sold it. As it had a musty odor. My question is what do I use to replace the old particle board original floor? My first thought is Marine Plywood? If so do I need to further seal it. I only want to make this repair once...It is 3/4 inch thick. I would use a Plastic material if I could find it. Secondly, what and (were do I get) the floor covering material? Vinyl ?? Finding where the water is coming from will be the next challenge but wanted to get the mold out as soon as possible. I am a person that likes to do things right the first time and I believe I can do a better job than hiring it done but I am not above asking ( paying for help ) if its above my capabilities.
Also, I have questions about the roof. I know there are many variables as to how long they last. I don't believe I have any issue with leakage at this time and I have used Dicor's lap sealant where I think problems could occur. I want to be proactive with roof maintenance, as I know how important it is. I am seeing small cracks (hairline ) over the surface. How should this handled ? I am enjoying this group and value the resource. Thanks in advance !