Its not necessarily "the way" to do it. It will last a long time, but with watersealed wood you can expect quite a few years worth without any issues.
But if you already have it, I don't see why OSB wouldnt work, as long as there are NO exposed parts. While I haven't had experience with this, something in my gut tells me a small amount of water would lead to some big problems with that kind of wood.
I vote go ahead and use it. Then report back so the rest of us can learn!