Just as data-points: The last 5 years, I've towed over 2000 miles per
year (including 3500' to 5000' passes in the Cascade and Siskyou
mountains) with my DG-300 in a metal-top Cobra trailer. My tow
vehicles have been a 2006 Subaru Impreza WRX and a 2010 Mazdaspeed 3 -
both with manual transmissions. The WRX was slightly better (given the
all-wheel-drive and better rear-weight distribution), but the seats
aggravated some back/spine issues I have and it had to go. But even
with the Mazdaspeed 3, it hasn't been an issue: I had a trailer tire
blow-out on the way back from Utah (outside Twin Falls, Idaho at 2am)
and was able to ease the car over to the shoulder without a problem.

--Noel