Tandem (and triple) axle trailers have a hard time with wheels and lugs because of the racking forces they experience being turned tight on a surface with good traction. Do you store or camp where you turn the trailer to nearly jackknifed on a paved pad? That's murder on everything down there, axles an all.
Are you replacing studs (and presumably nuts) only, or the entire hub? If studs, are they still a tight press fit in the hub? You should be able to get new studs from a quality American Manufacturer (not an American re-boxer of Pacific Rim junk). And of course match nut profile to the wheel.
Is the wheel damaged? This usually happens on the left side, since driving tends to keep the right side tight and loosen the left side. If the wheel holes are hogged out, and maybe the nuts aren't right too, seems possible to me to bottom the nut to, or right against, the hub flange, leaving not much clamping and centering action for the wheel itself.