The floor of a 12x16 shed is PT 2x6 on top of a PT 2x8 mudsill. The bottom
of the floor frame varies from 6" to 12" above the ground due to a ground
slope. The mudsill is on solid concrete blocks. The decking is 3/4 ACX.

Do I need to seal the underside of the ACX with thompsons water seal or
something similar? I've read a couple of differing opinions that floors
will rot from underneath.

Also, is it required to put a layer of stone under the frame? I packed
gravel under the concrete blocks but not the entire width/length of the
floor frame.

Thank you for your time.