I just got home with our new R-21 EC. Towed it thru about 60 miles of Atlanta traffic. It towed very well. I tow with a Toyota LandCruiser with all wheel drive, stability control and everything else available to help these old bones keep things under control. It has 6,500 pounds towing capacity, more than 250 HP and it's not a light weight SUV. I knew the tug was back there all the time, except downgrade. With all that weight, it picked up speed nicely (without me feeling the tug push the SUV) and then lost it all on the next upgrade. Winds were very strong here today, m/b 15-18 knots right on the beam. No swaying at all. Tractor trailers didn't affect us either.
I recall towing my J80 with a Toyota 4Runner several years ago. I was towing about 600 pounds less weight than the towing capacity. It was a load going up the hills and it pushed me down grade.
I'm comfortable with the LandCruiser' towing capacity and its capability to manage the load of the R-21, including stopping. I'd think long and hard about towing the R-21 with less than 5,000 pounds of towing capacity and a vehicle weighing less than 4,000 pounds. I tend to be conserative.
Gene