Pressure treated is treated against pests. You still have to weather seal it to protect it from the elements. Unfortunately, most of your people selling it don't realize that, when they are telling people that's why it's made for outdoor use. I was a Lowe's manager for 7 years and one of the first things I did when I transferred to a new store was to meet with the building materials employees and explain that to them. If your local store doesn't have any PT wood that's already dried, I'd just use regular plywood/lumber and paint and seal all 6 sides if it was for outdoor use. Now, there is some treated wood that is also impregnated with thompsons too, but I was never impressed with it.down here pressure treated just dries out and splits if you dont treat it with tompsons or something