Note re: getting it "adjusted"
I use a very established alignment shop, one of those 100+ year old family shops that still aligns everything and anything. They even have an axle press. But they stopped re-bending used axles. They'll add camber to new, but they became concerned over used axles, because one that lost its camber has probably been over loaded, and bending an axle back again makes it weaker.
Really, if a 3500 pound axle won't hold camber, it's probably time for an upgrade. For a single axle trailer, a runner torsion axle would be a nice upgrade. They transmit less shock, are self-damping, and increase ground clearance (no axle tube). Timbren and Mor-Ryde both off alternative rubber spring suspensions as well, which may last even longer than a torsion setup.