Alan,
Will Flex Seal Liquid or Paste stick on a long term basis to smooth dry plywood? I am not sure.
Remember also, that if the particle board he is talking about is OSB, OSB has some wax mixed into it by the manufacturer when they press it. This is required by code so that if it gets rained on once or twice during an installation job, it won't immediately turn into mush. So, I wonder how rubber products would stick to that long term.
Just some thoughts.
Thanks,
Mannyrock