Google a product called elevators. They are heavy duty steel brackets made to hold up a 2x4 2x6 or whatever joisted floor and accept 4x4 posts. They are angled out and very strong. Nail cross bracing to the 4x4 posts and you'll have no twisting.
Had a 5x6 two man blind with 2'6 joists and 5/4 deck board floor and 5/8 T111 walls on em out in Illinois for 5 years with no issues. Gave up that place and my buddy is in the process of taking it down to put it on another farm. The elevators also make a blind easy to disassemble if it needs to be moved.
Life Member of NRA, Tall Tine outfitters, and life member of UBP.