Looks good. I like to see how things are done differently in other parts of the country. You would never get away with filling the hole with concrete and just using a short piece of Sona tube on the top in these parts
The frost here would have a field day with the rough edges of the crete in the hole. Did you put rebar ladders in the piers? What did you use to support the insulation from underneath? OSB? When we built my buddies camp (very similar to yours so far) we used ISO ridgid insulation in the floors, the mice won't touch it like they will fiberglass.