I think you are all missing the point. The driver was just going too fast for the conditions or maybe had his cruise control on. If you have your cruise control on in heavy rain and the rear wheels start slipping the motor keeps applying more power to try and build speed causing the vehicle to start sliding. I don't think his tow vehicle is too small or trailer too big. I was hauling my F18 on it's own trailer with a Ford F250 diesel 4x4 on a wet highway (after a storm came through). The truck started to hydroplane all four wheels and the trailer started to jack knife I let the truck drift a little and lifted a little on the gas and the wheels regained traction and I kept on my way. The tires on my truck were not the best but did just past inspection. I think I had the cruise on and I was in the right lane where the road had depressions from wear holding water and I was going to fast. My truck weighs 7,500lbs and my trailer weighs about 1,200lbs. Only the driver will really know what happened.