Here in the Upstate New York, Marine plywood isn't something that jumps out at the home centers, and Treated plywood is toxic and generally anything but flat. OSB was just starting it's pandemic climb, and I could get 3 sheets out of the store at somewhere around $100.00. OSB holds screws better than CDX plywood, (so much of the interior is screwed to the subfloor) so that's how the decision was made. I took "ALL" of the shredded remains of the floor out except for under the bathroom. The special screws are available in various legnths, The drill point does not penetrate the frame however, and need pilot holes. I will use pocket hole screws to reinstall the furniture. I also felt the dimension of the subfloor was critical, because of the structural necessity of the furniture. which is why I did not go to the 3/4 advantech. The purpose of the resin is to adhere the OSB to the fiberglass, especially at the door which flexes quite a bit. Long answer to a short question.