Rhys has a few kits available with a temp switch for the fan built in like the link below. Its been a while since I looked seriously but I think this one won't fit but the next size down will. It will take a bit of fabrication work for mounts and the cooler will need to be on an angle, but there is plenty of space and there is spots to add an intake. Blank off around the cooler so air must pass through it - air flow will be from low front, move back and up.
I didn't end up fitting a cooler after I did a lot of live readings, even towing up mt glorious (very steep and slow with a 120deg hair pin at the bottom) my temp didn't go above 98deg. Around town it goes to 90 when foot is hard down from a green light and (immediately) drops to 86 once throttle is lifted. Highway with TC lockup it sits at 85-86. But for long periods of sand / off road work it would be beneficial.
The ecotune ecu replacement changes the way the clutches and torque converter operate - less clutch slip, earlier partial and full lock up on the converter. One example is - the ecu will alter between normal and sport shift maps to allow full lock up from 55ish km/h (TC locked with the sport shift map so it is running one gear lower but locked.) The TC is a huge source of heat generation, by locking, partial or full at times when it is usually open heat is reduced, by tweaking the cluch operation, heat is reduce through less slippage. However for slow off road work, or highway cruising it will provide no benefit.
PWR 6AN Automatic Transmission OIL Cooler 255mm X 280mm X 19mm With Temp Switch | eBay

