Jane Weeks, it must be code differences but weren't you allowed the option of a tank + drainfield combination? I've seen locally that more people are being "recommended" by the county to put in pump + mound + drainfield systems in order to protect water quality better.....somehow....in someway that I've not been properly informed. (??) Our local pump rate is $175 USD per tank and the drainfield allows for some extra time before that needs to be done. As Travis noted, anything to get that second tank under some kind of insulation. Around here (south and west of you on the other side of Minnesota) in low snow years, many seem to pile up straw bales on the tank which seems to help. With regard to grey water, we keep the kitchen sink still going to the septic tanks, but remember that any other sink/drain can, at a future time, be "judiciously redirected" as grey water with a little help from a Sawzall and some assisting friends with the know-how.
The water table here is too high for any kind of drainage system. If I had the money for a regular septic system, I'd have to have many, many truckloads of soil brought in (difficult to get to) and have a new well drilled as well, as it would be too close for modern laws. I've piled lots of straw on top of the second tank and I'll keep my fingers crossed when it gets really freezing. I hope that in the future I can redirect the grey water, as you say "with a little help from my friends."