I have been using this in both boats and RV's for at least 15 years. Currently the RV has a large piece which sits behind the front windshield, and gives definite decrease in interior temperature. (also holds heat in). I also have styrofoam, with reflective foil on both sides, pieces cut in sections to cover the same area, and if very cold or very hot, I use both.
In the C Dory 25 and Tom Cat, I had pieces cut for all of the side windows. Especially in the 25, it made a huge difference in the air conditioning ability to cool the boat. For example in 105 ambient, I got the interior down to 80 degrees, with a 5,000 BTU "Arctic King" window unit. I am sure that the C Dory 22 would respond the same way. As for Powell--we had not used it there, since we have not used the Air Conditioner at Powell. (except at the camp ground). We feel that leaving the windows open and having good air flow is better, but shade is certainly important--and it might well be worth while cutting a set for the side windows…Good idea! We did line the sides of the V berth area with back packing pads (as well as under the mattress. This seems to have made a significant difference in both temperature in the evening in the V berth, as well as apparently less condensation. I am not sure the foil/ air bladders would do the same on the side of the hull, but the stuff is cheap enough that it might be worth an experiment.
We do use the styrofoam foil covered material for the top of the ice chests and freezer when traveling and at Powell. I cannot say how much this helps, but I am sure some.
