I have the Marathons on my 17' Sea Class TDB and love them. I have pulled the boat to North Carolina 3 times, North Dakota once, and all over Alabama over the past 3 years on them without the first problem. I have, however, heard internet chatter about some folks having issues with them. I upgraded from the 13" tires that came with the trailer to 14" tires that I am running now. I feel that getting the largest tires possible reduces wear and tear on everything else on the trailer/axle/hubs/etc. I also have a set of 15" Marathons under my flats fishing boat -- too many trips to the Louisiana coast to count and no problems with them either.
Keep the hubs greased and the pressures correct. Also, it would ease your mind to double check that your axle is correctly aligned and straight.