I personally think if you're going to do DIY, and apply hundreds of dollars or more of sealants and other products to it, you should not waste your time with something so disposable as plywood. I fully expect to get flamed for this...but it doesn't take much to destroy plywood, rending your expensive coatings wasted. If it bends, your coating is likely to crack.. if it gets wet, its likely to swell and/or delaminate and it'll leak..
There are plenty of success stories.. but a lot more failures. I would stick with something more permanent.. concrete or concrete block or solid woods.. things like that. Unless you're talking small scale, in which case its not even worth doing t in the first place.