krusen

Here's a link showing the cooler on an earlier gen Odyssey. My 2008 was in a similar location; in front of the radiator catching gravel coming in through the air dam. Picture 39 on this PDF shows the unfinned factory transmission cooler tube snaking across the radiator.
http://handa-accessories.com/odyssey/05tow.pdf

Interesting item is that the Power Steering cooler was noted as being as important as the transmission cooler. The logic cited was that when towing, you're going to be in a lower gear running at higher RPM's. These extended high engine speeds will overheat the power steering fluid due to frictional as it circulates through the pump.

Thanks to others for the map suggestions.