I had an after-market transmission cooler installed that is larger than the strange looking little one sold by Honda. The van already had over 80,000 miles on it when we first started using it to tow last year and installed the cooler. I have read reports on the Honda forums of trany problems, but we haven't had any issues. I had the transmission fluid completely replaced at around 80,000 miles (should have done it sooner) and again this season before leaving for vacation. Apparently it takes special equipment, but the trany shop claims that they can replace all 11 quarts of fluid where I can only replace 3 quarts if I do it at home. I am going to spend the $85 every other year and have this done just to be safe.
I did not install the power steering cooler--the trailer is right at the lower limit (~2,000 lbs.) where they begin to recommend it. I guess I would be more motivated to do this if I better understood how the functioning of the power steering unit was affected by towing. Also, I haven't seen reports on the forums of it failing.
The issues we have had were an EGR passage clogging up--covered by warranty for most folks, but not us as ours is a Canadian model brought to the U.S...., and electric door problems.
Derek, only reason I mentioned the PS Cooler was that once you put a WDH on it throws more weight
on to the front wheels and then the ps fluid gets hotter, I did both on mine while I was at it