in my limited experience (3 trips, about 100 miles sailing alltogether) the drive unit is not a problem at all on my 26 ft boat. The problem is the course computer. My course computer likes to take a siesta whenever it gets a little warmer. It will simply "go to sleep" without warning. Very annoying.
So, I am considering an upgrade, I have two old CPU cooling fans, will make a couple holes in the box and make them blow air in and out.