I haven't read of that many problems with towable's running gear, other than a lot of tire problems. It seems that there are a lot of garbage tires out there. Although I imagine a number of problems could be blamed on the RVer due to overloading or running at the wrong pressures, or any number of other issues.
As an example on tires, I remember a number of years back, many swore by Goodyear Marathons as the best tire out there. In the last few years many people have been swearing at them. I honestly don't know what the latest take is on current Goodyear Marathons.