I finally added a second cooler. It's a B&M Supercooler model number 70268. It's mounted but I haven't connected the lines yet.
I've been wanting to do this for some time now. The transmission fan I added a couple years ago helped a lot but wasn't enough. I got tired of "driving by the transmission temperature gauge." I monitored it closely all of the time while towing, drove in 3rd gear to keep temps under 180, watched my RPMs in 3rd being careful not to drive too fast (high RPMS). I had to run the transmission fan all of the time while towing. All of this made for a stressful tow when taking the boat out in the summer.
I've seen a lot of posts about locations and space to mount a second cooler so I'm posting some pictures. This cooler measures 11 x 7.25 inches. I could have fit a bigger cooler. I have plenty of space in front of the cooler for a fan in the future. I tried to pick a location with the most air flow. This location actually gets more air flow than the stock cooler because it's higher behind the grill.