Couple thoughts.
Soda bottles and the like are gas permeable. It isn’t just that the lids leak, gasses pass through the plastic. They are not ideal for long term storage because of this.
Using dry ice to evacuate oxygen might work in AZ, but in NC the water vapor in the air condenses on the dry ice, so I’d be sealing in a lot of moisture. I don’t know, but isn’t the fog from dry ice really very fine water droplets…like in real fog?
If you’re buying 6 months worth of flour at a time, storage isn’t too critical, any sealable container kept in a closet will be fine. I still freeze it first. Speaking of which, I seal it first, then freeze so as to avoid any condensation on the product when taking it out of the freezer.
Oxygen absorbers are great, but the guys that make them say not to use them in combination with a desiccant. Your humidity is so low that you wouldn’t bother, just wanted to point it out.
FWIW, I like glass containers in the pantry, even though they are fragile. Mylar bags in buckets is probably better if you’re stacking really deep.