When I started looking for replacements I did a bunch of research on each of the tires I thought I would consider. With the exception of Kumho there wasn't a single tire that was rated for high speed or didn't have a host of comments about poor quality and blow outs. Trying to get the Kumho 857s locally was very difficult so I went back to the Marathons. I had them mounted, balanced and filled with nitrogen. I also went through the trailer to ensure the brakes where working correctly and the calipers were not hanging in effort to ensue I'm not adding heat from any other source other than the road.
I have a 250 mile trip planed for Friday that will test my new set up so we'll see how things go. I do say though that I feel confident with my set up. I have a tandem trailer with an X2 so weight shouldn't be an issue. The brakes and bearings have just been serviced and the tires are balanced and filled with nitrogen so everything on the rolling stock should be as good as it can be. I always plan my trips to leave early in the morning and as in this case typically arrive before noon as to avoid the mid day sun/heat. Temperatures in Michigan seldom go beyond 85 degrees at the times I'm driving so heat should be well within the tire design limits.
As bad a name as the Marathons have received I have (knock on wood) never had one fail and I've had these tires on the last three trailers over the past 15 years.