All the information you will need to maintain your axles is in this manual. Greasing the bearings is only recommended every 12,000 miles, at which time it is also recommended to inspect your brakes by pulling the drum/hub assembly. If you pull the drum, grease the bearings at that time, install new seals, and you will be good for another year. By pumping grease in the axle, you risk leaking grease into the drum and getting the brake shoes and magnet contaminated, which will cost much more than just doing an annual maintenance.
http://www.dexteraxle.com/docs/defau....pdf?sfvrsn=26