Here are some pictures of the finished product. I painted it all black so that the sun could also contribute some heat. Since the chimney needed to be higher than my coach it needed some support so I rigged up some metal supports.

[Linked Image from i1288.photobucket.com]

[Linked Image from i1288.photobucket.com]

Last year I used a cheap duct blower fan to circulate the air through the ducting. It worked ok but was quite noisy. I am now using a quiet 8" computer fan. I have the fan run through a timer that I have programmed. It seems to work better to have the fan shut off periodically to let the sand immediately next to the ducting reheat itself from the mass of hot sand in the overall structure. I get an average temperature of 100F from the duct outlet into my coach. Once the sand has been fully heated it will retain it's temperature for literally days. The idea is that I shouldn't have to burn as much firewood as there is not near as much wasted heat as last year.
There has only been one real problem with this idea in its current form. My oil drum wood stove has not been strong enough to hold up to the extremely high temperatures in the battery. Especially since it is encased in heavy sand. It has basically been collapsing in on itself so I have not been able to use it for the last few weeks unfortunately. Luckily the weather has been fairly mild for this time of year. The new stove will be a modified old large cylindrical propane tank found here on the property. It has been evacuated of any gases and is ready to have one end cut off to be made into my new stove. It is made of quite thick steel so it should be robust enough to hold up. Sorry I don't have a picture of it right now but will post one later. Everything is on hold right now because of the Christmas season. My friend Denis and my brother Scott have other commitments of course. I'm surviving fine with electric heaters and the diesel Aquahot system for now.
You may have noticed in the above pictures that I have changed the way I have skirted the coach. I invented this idea myself and am quite happy with how it has worked out. I used styrofoam board supported on 2x4's that I installed dowl pins into. The styrofoam boards fit between the dowl pins. The 2x4's each have a single large spike through the middle holding them to the ground. The 2x4's can pivot on the spike as well. This helps when removing boards that have exhaust pipes ported through them. Bungee cords also keep the boards secure to the side of the coach. I have painter's tape strips on the coach where the boards lean so the gelcoat wont get scratched up. This set-up will allow me to start the coach if I want. The air suspended coach can rise up and down behind the skirting. My heat battery ducting will have to be temporarily disconnected to do this however. The styrofoam boards can also be independently removed for access to baggage bays and compartments.