I wouldn't be happy running an auto thousands of miles in sports mode, it really indicates the tow car is under powered for all road conditions, I would think it could be used to maintain higher revs for uphill stretches however, if it works for you so be it.
What would be interesting is to rig up a temp sensor on the auto box or the cooler and see what it's doing while towing. You could then determine if the standard cooler is doing a job or not.
