There is a an excellent explaination of the benefits of different types of foil installations at the following web-site:
Some thoughts or conclusions that I have after gleaning from the above site and others are the following:
1.) Even though an airstream has a relective skin it is not nearly as relective as highly shiny foil insulation. In the case of my belly pan I doubt it is all that effective as a relector (and never will be). If it is true that the aluminum skins are really that reflective and that such a large percentage of heat loss is reflective then we wouldn't be talkaing about the need to insulate at all.
2.) A very well polished airstream skin will in fact have less heat gain in the summer.
3.) Where the foil should be placed for best effectiveness depends on whether we are trying to keep heat out or keep heat in the trailer. I think this means that the outer surface of a well polished unit will help keep heat out but does not really help keep heat in. Maybe we should polish the inside of the skin as well?
4.) Foil seems to work best when its relective surfaces are not in direct contact with anything but air.
5.) There are 3 types of heat transfer mechanisms that all need to be considered to some degree (conduction, convection, radiation). Evidently 65% to 85% of heat transfer through walls is by radiation and up to 93% through floors.
6.) Reducing heat loss is not just a case of having a high R-value since R-value seems to only apply to heat transfer by conduction.
Some practical application thoughts:
If it is true that 93% of the heat loss through the floor happens through radiation then it seems like underfloor insulation could be accomlished quite well without actually sealing up the floor to air flow. What appears to be needed are at least two reflective surfaces - one pointing toward the interior and one toward the ground - somewhere in the underfloor cavitity. It seems to be preferable to have an air gap above and an air gap below the foil. Since the underfloor area seems to be quite capable of getting really dirty I think I would want to keep the foil near the top and try to block dust from getting onto the top surface of the foil (reducing its reflectivity). So I think the question still is how best to mount foil an inch or so below the floor. Maybe using sticky back foam tape might work? I think I would still want to have the area above the foil mostly sealed but still leave a weep hole or two for condensaction to drip out. It might make sense to staple a layer of foil directly to the bottom of the floor and add another layer about 1" below the floor. The layer on the bottom of the floor would help prevent moisture from attacking the floor and would give an extra barrier to summer heat gain.
From the examples given in the tutorial I sited above I think it would be great to have two layers of foil in the wall cavities. It is interesting to note that their example wall was only 1-1/2" thick. Again would sticky back foam tape be a good machanism for suspending the foil in the middle of the cavities?
I like the idea of some sort of proactive ventilation mechanism for under the floor. My son-in-law suggested installing a small fan under the floor that could be used to power vent the area. I am also aware that you can buy round louvered vent covers with a built in screen that are designed to be used in the soffit of your house (on the bottom side of your roof overhang if you are not familiar with the term soffit). The ones I am thinking of are made out of aluminum and are about 3" in diameter as I recall. The louvers are all nicely pointing in one direction. I think I will at least consider using some of these vents and maybe the fan too.