Brakes wore out on 3 out of 4 wheels, in a distance that a aggressive diver could go thru a set of shoes,(considering trailer shoes start much thinner than back in the day when a high performance car had all drum brakes, the mileage is not that far out of line). Now you want to tell the world the most likely problem is with the 3?
If the OP has had a bunch of trouble with bearings and blowouts, I would look into "Are brakes getting power when they shouldn't", but with the info I have the first thing I would look for would be 1 of the no-strip Scotch-lock connectors. Next would be where brake is grounded. Next would normally be check right where wire connects to magnet. (Had drum off, should of checked then) Next look at connection where that wheel Ys off the others.