Tell him to learn to use the manual override on trailer brake control in stead of hitting the brake pedal to stop swaying. He'll need it when that second and third tractor-trailer in a row pass him on the interstate. Been there, done that.
One year during spring canoe season I was towing an 18 ft 2800 lb when empty trailer loaded and had more gear inside a 1991 Isuzu Trooper along with the large cooler on the front bumper. 3 tractor trailers north of Richmond on i-95 past me on the left. First one push me over a little. Second one push me over more and I started to sway. By the time the third one pass me the sway increased to the point that I knew I was going to lose it. What's save me was keeping my foot on the gas and hitting the manual switch on the brake controller. When the trailer brakes engaged it's snatch me straight and I let off the gas until this way was gone.
After that I kept an eye on the mirrors watching the tractor trailers until I got off at Fredericksburg. I learned a serious lesson about sway control and too much trailer and gear.
Yes I could tow it but shouldn't have been.
After that I bought a pop up for spring camping and only towed the trailer empty during hunting season. I made two trips to set up hunting camp. One trip to drop the trailer, second trip was with a utility trailer and my camping gear.
After I bought the Silverado 1500 no more problems towing either.
I now have a 28 foot trailer that is 4500 lbs dry.