Nick Let's replace windows with outdoor cameras and computer
Nick projectors or flat screen TVs, with fluorescent lights and
Nick doors or push-out panels for fire escapes.

So you see how untenable this position is.

I was thinking a little more about the OP's issues heating his house.
It sounds like he's on a south-facing slope. Some of the slopes in
that area are steep enough that his lower floor may be off the ground
on piers which are illuminated by the sun. Alternatively, there is
2000 ft^2 of upper floor not over lower floor, which may also be on
sunlit piers.

In either case, he might be able to build one of your solar closets
down among his sunlit piers, then use air blown through that to heat
the house at night. It would make the house much more usable, increase
resale value, and aesthetic issues with DIY-built stuff would be less
important since it's out of (his) sight. Also, in that neighborhood a
homebuilt solar closet may not generate adverse comments from the
neighbors.

If he can pick up 600 BTU/ft^2/day in February, store it through much
of the night, fix the worst of his air leaks, and add some attic
insulation, he might get half his heating done with 400 ft^2 of solar
aperture and 500 gallons swinging between 90 F and 140 F. That'll save
a bundle on the replacement furnace and the bills from same. Depending
on the house configuration, there may be 40 lateral feet of sunlit
piers down there, so there is some chance of fitting significant solar
aperture. On steep hillsides, angling the solar closet glazing
slightly (15 degrees) face-up from simply vertical can greatly increase
the vertical extent of the glazing without chewing up a lot of real
estate. He might implement a 10 or even 20 foot tall face for the
collector.

If I were going to do any such thing:
- I'd get a contractor to build the footing and concrete pad
under the house for the heat store. Someone used to
doing foundation work, who won't screw up the existing
footings. Have them drill a pier to bedrock if necessary.
- I'd go big on the heat store. 1000 gallons if you can manage it.
- Use 55-gallon (or 40-gallon if you can get them) used plastic
barrels to store the water.
- Build the glazing as tall as possibly practical. It doesn't weigh
very much and often people don't use steep real estate below
their house.
- Heat the water directly rather than use an air heater to transfer
heat to the water. The EPDM mats seem like a nice solution,
but you'll not like the $5/ft^2 price.