Looking to heat a winter greenhouse

I would like to build a passive solar greenhouse, and grow food all year long.

~enter reality check~
I live in southern Vermont, on the north side of a mountain, 1300 feet up.  We get a lot of cloud cover in the winter.  So I'll either have to settle for a season extender, or figure out some way to heat it in the winter.  I'm looking into some solar, but I won't be able to depend on it.  I've thought about a rocket mass heater, but I've read they aren't really suited for greenhouses.  Greenhouses aren't insulated enough to hold the warmth.  In case it matters, I plan on using glass.  I would love to use double pane if I can afford to.  I also plan on growing cold tolerant crops, so I'm hoping  to heat to 40-50 degrees F.

So I've been thinking.  I can use barrels of water to trap the day's heat, but not if the greenhouse doesn't warm up.  But can I use a rocket mass heater and water tubes to 1) warm the soil in the raised beds and/or 2) to heat the water in the barrels?

I have a high tunnel that I heat with a box stove using wood.   I do have good southern exposure and protection from the north. I keep a couple hundred gallons of water in the tunnel.   When the temperature drops below 20 f I need to use the wood heat. Usually, this is 11 pm to a couple of hours after sunrise.   I do not bother to heat in Jan and Feb.

I have discovered a source of bubble wrap and am considering sandwiching to between layers of plastic.  I am not sure it will be worth the effort, but it would be an interesting experiment.

I built a 4" J-tube in my glasshouse, which is 15 square meters and is dug into the ground 75 cm for extra height and thermal flywheel effects. The small cob bench stores enough heat that I can run it for 4-6 hours ahead of a night with freezing temps, which in this region are rarely below -2C. The inside stays at least 5 degrees warmer than the outside, and this is in spite of the thin glass providing next to zero insulation. I burn about an armload of wood to do this, maybe 4 kg of dry hardwood on average.

In Vermont, you'd need a bigger system and ideally a better way to prevent heat escaping. But it's certainly possible.

I have no personal experience but a lot of interest in this subject.
The one thing I encourage you to do is to separate the thermal mass from the earth below.
I've seen builds that  run ductwork directly in the soil of the greenhouse and they seem to perform poorly.
Soil can be a thermal mass but unless there is an insulative perimeter you will be heating the entire earth, and that is a losing prospect.
By heating a bench that is thermally isolated from the earth, you can raise the temperature of the air,plants and even soil, through radiant heating.

Following on from what William mentioned about thermally breaking the mass from the ground, my cob bench sits on concrete and rubble with air spaces between it and the ground. So there is some heat conductivity via the concrete, but not a close coupling to the earth floor. This feature also helps to mitigate moisture wicking into the bench from below.