Even though Yakima is based in Washington, I wouldn't be surprised if they are now outsourcing some parts (i.e.,China). Wouldn't want a failure while underway...
Don't know if they would be stronger, but you might want to cut down some trailer "U-bolts" and give it some stress and check before mounting. Beyond that, you could go to a machine shop and have them make you a set out of grade 5 or 8 steel...