I have a Nash 25-S travel trailer that came with ST 205-75-15-C's & bumped up to ST 225-75-15-D's from Towmaster (Greenball). They are now Chinese made (used to be made in Canada on the Goodyear Marathon assembly line).
I've ben trying to find an LT 225-75-15-D, with no luck. Just not made. I seem to be stuck with the ST's.
What I have done is to change out the tires every 3 years & keep them covered. I live in Phoenix, AZ. where the climate is hard on rubber. My system seems to work as I have never had a tire failure. Every year, I tow my trailer for a 2 week trip, with no problems. Worst case scenario is that you might consider doing what I've resigned myself to do. It works for me even though it's not as good as I'd like.
The 65 mph. limit is not as bad as it sounds. My '03 Dodge with 3:73's is designed to be most efficient at 1800 to 1900 rpms, according to Dennis Hurst the head engineer at the Cummins Engine Plant. Those rpm's, with stock sized tires, puts me between 62 & 65 mph. It's been my experience that the slower you go, the better mileage you get, towing. While on Hwy 99 between Bakersfield, CA. & Sacremento, CA. I got 3 fill-ups over 15 mpg. while towing my trailer. Hwy 99 is a truck route that is very flat & has a speed limit, towing, of 55 mph. I got in line with all the trucks & we were usually doing about 57 mph.
This system works, for me. An arctic Fox is an excellent trailer. I've had my Nash (not quite as luxurious as the A/F) since '98 & have towed it from AZ to Ontario, Canada, WV. , WA. , CA SD. , & in all the Western Mountain States. It's been almost completely trouble free & very comfortable. The tires do get used. I'd buy the A/F & deal with the tires later.
Joe F.