I figured I would review my recent purchase. After having two Goodyear Marathons de-laminate on me, I went with Tow-Master tires from Greenball. The boat tires that came from Mastercraft were load range D, so I purchased those in a 225/75R15 size. I paid $150 for 2 shipped off eBay. When they were mounted, the installer balanced the wheels. I don't know if this is necessary, but it can't hurt. I also run them at 65 PSI.
I have since towed about 500 miles, and wanted to share first impressions.
On the highway at around 60 mph, these tires are great. The Marathons used to sway after hitting expansion joints or rough spots. These are straight and true. They seem to be riding much smoother, as I can barely feel the trailer in the car, where as it used to bounce and bang around. The trailer used to sway enough at 65/70 that it would move the car. Now it is perfectly straight and true.
Low speed driving:
Similar to the highway, the tires appear to be much softer and smoother riding. The trailer is not unsettled by pot holes, and does not bounce around.
Huge improvement in tracking and ride quality. I can barely tell I'm towing a boat now. After ~60 miles on the highway, the Marathons used to be very warm to the touch. These are nice and cool. These tires are GREAT.