GBR - i planned on doing all of those things including wrapping sono's with plastic (6mil vapour barrier in my case cause that's what i got lots of on hand) except for the 2" insulation boards. not sure what you meant here.
this is what i interpreted:
i should form a 4 sided box out of 2" thick ridgid insulation with each wall being 1' deep. then slip this box over the sonotobe such that it forms an insulated barrier between the earth and the gravel backfill. it its just below the surface of the soil, i.e. is flush with grade.
birds eye view attached
otherwise, it seems the advice basically resides around finding ways to keep the soil from freezing prior to pier concrete pour and during the curing period (10 days?).
what about add mixtures like an accerlant?