I disagree that a finned tranny pan will not make much of a difference. The reasoning you gave about not having any medium (air) to send the heat to is, in my opinion, not valid. As long as there is a sufficient volume of air under the vehicle to absorb the heat, the increased surface area of a pan with fins, or cooling tubes, will make a substantial difference. Even at the very slow trail speeds, there is constantly a fresh supply of air under and around the vehicle, and this air will "absorb" the heat as long as it is cooler than the pan is. For another reference, I believe FourWheeler magazine had an article with their project Blazer (the blue diesel one) a while back when they tested several different types of transmission mods and reported the cooling effect they had.