Tires have always been an important consideration for RVs, and perhaps even more so for tires on heavily loaded single axle trailers. We'd only had the Scamp for six months when I installed a set of Maxxis UE-168 light truck tires to increase the safety margin. By the time we headed to Alaska, we were already running into availability issues.
On our return from our Alaska trip, I switched to 15" rims with Continental Vanco 215/70R15 tires that have provided excellent service for nearly five years, but once again, my tire of choice is no longer available! Apparently, Westfalia owners have switched to 16 inch rims to get higher capacity tires, reducing the marketplace for the specific size I need.
Goodyear quit making the Marathon and introduced a new design, the Endurance, for the trailer market. They make them in the US. They've been out for a couple years and have very positive feedback.