You indeed have a quandry.
Goodyear Marathons "So highly recommended" have a bad habit of suffering belt seperation due to overheating. They are only speed rated(a European convention) to 65 Miles Per Hour(MPH). So at 60 MPH you only have a 8% safety margin. Lt tires here are generally speed rated. they are usually around 99 MPH. Those of us who have had these "superior", "highly recommended" ST tires come apart with tire pressure monitering systems installed and know that the tires were not underinflated until the belts seperated, have come to the realization that the 65 MPH rating is just not enough.
The speed rating is an overall acid test of the tires ability (under full load and speed rating) to generate heat, dissapate heat and not come apart with the heat that it could not dissipate. That being said if a tire can survive 99 MPH at full load then 62 MPH (38% safety margin) is a piece of cake. I did a lot of research including talking to the Engineer responsible for the testing procedures (a United States Federal Employee working for the National Highway Transportation Safety Adm.). His advice was to select the highest speed rating available, not because you are going to run 99 MPH, but for the safety margin. My 31 foot Excella originally had Michelin XCA 7.00/15s, which was an LT tire. The BF GoodRICH Commercial TA LT225/75R16 that I went to (along with new rims) is the same Outside diameter as the original XCA and the width of the Goodyear Marathon ST225/75R15.
My recommendation is simply this.
1. Determine what size tire came on your trailer originally.
2. Email the manufacturer of that tire and request the outside diameter (OD) and Maximum tire width on on the original wheel(usually 6 inches wide.) and load range. They have this information on record, trust me.
3. Email Michelin or B. F. GoodRich (now owned by Michelin) and see what they have in your specifications.
4. Considering the cost of having a body panel replaced, I also recommend a Tire Pressure Monitering System.
I have only presented an alternative. The choice is yours.
Here is the latest thread on this subject.
If you have any questions or want assistance, feel free to email me and I will do my best.