I've never seen ANY propane appliance freeze in the winter ever and it gets COLD here. Propane appliances (including standby generators) run on vapor, not liquid and the dip tube in a residential propane tank ONLY pulls vapor, NOT liquid. Why a full bottle is 85% of total liquid capacity, there has to be space above the liquid for the vapor to be drawn from.
Underground is ok, until the tank gets a leak in it and then the only way you can tell is all the dead grass around the tank and that takes some time leaking to happen. I much prefer an above ground bottle. Easier to check the level on as well.
Both mine are owned and both are painted hunter green Rustoleum. Blend right in with the trees.