I can't say you need one but having one the right size installed correctly can do nothing but help. That plus an add on spin on fluid filter, too if you install the cooler.
Make sure you stick with Honda fluid and never use anything labeled "Universal". There are some high quality synthetic fluids out there that work just fine but if you're not informed about this kind of stuff and not 100% sure of what you're doing default default back to Honda fluid.
...and everyone knows how to drive carefully and this situation is one of those times. You'll still make it to where you're going even though you'll be a few minutes behind.
And last, get some test drives and visual inspections done before ever considering taking off on a trip. Check the fluid lever exactly as described in the owner's manual.
Don't take anyone's advice that is different from the manufacturer unless your sure you understand all this.
I used a $65 IR gun to check temps on my V8 4Runner after driving with out a load and also towing a loaded horse trailer on a summer day in the desert. I did not install a cooler because the temps using Red Line D4 were right in line with what was expected.
I switched away from Toyota fluid because I was familiar with the requirements and the performance of D4.