lag bolts, preasure treated woodand joist hangers are the way to go. Build yourself a fortress up there. Better safe then sorry. I would feel safer in a structure I built, rather then something mass produced in china. They can't even make dog food or baby formula without killing us.

This past Saturday, I moved a 16 foot ladder stand bought from Wally World, one year ago. The entire seating platform and shooting rails had become unattached from all the bolts and brackets rusting apart. Junk stands. Wejust built a tower stand using all the materials you have described, plus some TREX for the decking and a roof oner top. Our tower stand will outlast any store bought stand. With a little primer and paintitshould last a life time of hunting.