Looking for Transmission Oil Cooler suggestions.

2001 XJ w/o Factory Tow Package

I will be towing a 3500 pound travel trailer.

I have two trans oil coolers (not yet installed)-
One a B&M "Super Cooler" rated to 16,000 pounds gross combined weight (size 5"X11"X1.5")
One a Derale rated to 20,500 pounds gross combined (size 11" X17")

The B&M is a stacked plate, twisted tube design, supposedly very efficient.
The Derale is a regular tube-and-fin type.

I can barely fit the 1.5" thick one between the grille and the AC condensor, but it will block fewer square inches of the radiator.

Question (especially to those who tow):
While both my coolers are bigger than the very small OEM towing oil cooler (as included w/ the tow package), which one (based on experience) would YOU use?

Have you had your XJ overheat, or the AC become inefficient in hot weather while towing and using a trans cooler that is mounted in front of the radiator?

As far as installation- I live in a warm climate, so I plan to hook the aux cooler in series AFTER the heat exchanger in the radiator tank.

Is the transmission return line from the radiator heat exchanger (that I want to cut into) the TOP one on the radiator that then routes to the REAR transmission fluid line?

Bob

Generally the finned coolers are better at cooling fluid then the tube coolers. I'd use the finnes cooler for just that reason. I can't input on the A/C because i cut mine up and now it's OBA! Oh and my A/C is a lack of doors in the hot weather...very refreshing.