Greenhouse as passive solar housing shell

I currently have a 70's airstream set up on my property as my primary homesteading residence. It's really a 2.5 season setup because late in the fall temperatures get low enough to freeze everything so I close it up. I recently had a thought that I could erect a 30 x 30 poly greenhouse around the airstream to protect it from the winder elements. I also have a passive solar collector I've been working on to provide hot water, but I thought that if I could purpose it an grab a couple IBC totes, I could use that system to provide some thermal mass. Coupled with the temperature gain from the plastic, my thought is that it would provide enough warmth and thermal mass  to keep the Airstream above freezing during the winter. If I want to use the space I could supplement the heat inside the Airsstream with a propane heater.  In addition to the heat gains, it would provide a nice environment for starting plants in the spring as usually I can't put them out until June 1.

I've looked into the double walled poly tunnels, and it seems like the insulation value is great, the only issue I can think of is that I don't want to run a fan constantly to keep it inflated. Are there any alternatives to forcing air between the layers? I was thinking that maybe if I took some packing material ( those inflated bags they use to pack in boxes ) then perhaps I could string some of those bags in between the the layers at intervals which would keep the layers apart and provide a similar insulation factor.

Any thoughts on other things I could do? am I overlooking anything important?

I read of this being done before.
That couple had a wood stove, firewood, couch and rug in their hoop house, doing side their camper.
They used shade cloth overhead during the summer,  and opened the sides for ventilation.
They even overwintered ducks in one corner.

Separating layers without a blower might be accomplished by running clear vinyl tubing between the layers, using plastic bottles,  bubble wrap or other mechanical means.
There are tough, insulative pool covers that have been used as well.
The advantage of the blower system is the minimal amount of contact between layers,  which prevents thermal bridging.
Another idea is to build nesting hoop houses.

The hoop house is such a good idea,  but in addition,  you could insulate the outside of the camper with anything from stonework to cardboard.

In all cases,  watch for fire hazards.

1) Radiant Heat supplement inside the airstream (heated toilet seat/keyboard/etc) (Feels like +20F)
2) Regular Heat (+ as much BTU you want to add)
3) I would use haybale all around the airstream to insulate it. (+10F)
4) 1st Hoop House (+5F)
5) 2nd Hoop House (+10F)

The Amish use these spacer block things.  They are a plastic box about 10 inch cube.  The bottom had a semi circle cutout to fit the hoop and holes to zip tie it in place.  You need one every 5 to 8 foot of bow. They are surprisingly expensive.  You can probably put up a second frame cheaper.  The inner frame can be really minimal as the outer frame will take all the wind.  I figure a hoop every 10-12 feet and one purlen on top.  

I hope to build a greenhouse using a modified hoop setup; I am planning to build trusses of a sort, and this will provide enough separation that an interior membrane  would be well separated from the exterior one. More fuss.. Worth it to me for added strength.

A well insulated north wall would be a nice upgrade; I am think old panels from walk-in freezers.

I think you would want to take some care with the exhaust from propane appliances... including those built in to the airstream!