Hal,

Because these trailers are normally pulled on hiways, I would expect hi-mileage brake life.  
Two axles should have two sets of brakes normally.  I assume TM does this.  This means twice the swept area of the brakes and more braking power.  If the brakes stay cool their life will be exceptional.

Either the brake controller is not set up right, the brakes are not being adjusted right, or there is some unusual driving condition involved.  A long downhill braking situation could eat up the brakes if they overheat.