Ken,
I know you've already got a plan, but I'll put this here anyway just in case it ever comes up future searches.
As David mentioned, I'm running a Seatrab plate&frame style cooler that I originally purchased through Art Carr a long time ago. It is mounted at a 45° angle from the ground under my battery on a piece of aluminum that I bolted to the frame through existing bolt holes. The cooler is approximately 6" x 12" x 2"thick and came with twin 6" fans. I then added some stainless steel ducting to one of the bumper openings (for air to enter) and opened up some of the fender liner (so air can exit).
I was concerned about taking my car and entire family on The Epic Drive and how the 3500-3800 non-locking converter would handle the extra load and long steep grades. There were a few long hills that I could watch my transmission temperature climb as the hill continued, but my transmission never went above 195°F and then recovered to 180°F pretty quickly. The ambient temperatures weren't very hot, so I am slightly concerned if I did a similar drive in 100°F temps.