I put together a portable storage building whose siding was all particle or wafer board. It came in a kit and the board was already primed. I usually use Color Place semi-gloss latex paint on my house and I put it on the storage building also. That was about 10 years ago and it has held up well. If your wood hasn`t been primed yet of course you should do this first. I use KILZ primer. It is pretty thick for primer I think. See what you think and you can thin it down if you like so that it will flow easier into the seams made by the wood chips when they were pressed together.