There might be a sticker on the trailer with the GVWR and perhaps other useful information. All new trailers have one, but with a vintage trailer, of course, it may no longer be present.
In the absence of the sticker I’d hazard a guess the empty trailer weighs around 1100# and rides on a 2000#
axle, giving around 800-1000# of cargo capacity. Load to maintain at least 12% tongue
weight.
For carrying a heavy load, make sure your
tires are at least load range C, less than 5 years old, and inflated to maximum sidewall pressure.
Check your vehicle manual regarding trailer
brakes. I’m guessing the
Campster doesn’t have them, and many vehicles and a few states (NY among them) require
brakes over 1000#.
In addition to bearings and running
lights, a few other things might be worth checking on such an old trailer: (1) coupler adjustment, (2) frame and
axle, and (3) bolts holding the shell to the frame.