As a builder for 35 years I can say treated lumber is junk, lowest grade they can get away with. You will also end up with 1 grade less than a normal stamp if you buy at a box store. Treated is also hard on fasteners. I just replaced a floor in my lund the plywood was ok but all the fasteners rusted away causing failer. J B has a great suggestion if you can find some exotic wood . I wood stick with good grade pine and treat it yourself. Glue and screw everything. Keep the moisture out and you wont have a problem. Easy to say I am facing the same issues myself need more time and space.