OK so am going thru the new to me 5ver since being used you don't really know,Its my 1st trailer of any size anyways and the first with brakes, My sprinter has two axles and while I was packing bearin...
Check the front brakes to make sure they are properly engaging. If not, this may be a reason for extra wear on rear brakes. You can check for loose wires going to front axle, check them with an electric meter to make sure they are getting juice, or just jack up one side, have someone apply the brakes and try to spin both front and rear wheels. If rear wheel locks and front doesn't, therein lies your issue.