Somone over on the FGRV forum posted this and it seemed worth repeating.
Trailer Boats magazine are issuing a 'Trailer Tune-up Guide' as a free leaflet at West Marine stores, or it's available online. Obviously it's directed towards boat trailers, but bearings is bearings, whatever they're on. They also cover things like brakes and lighting.
TrailerBoats Tune-up Guide
Bearing repacking section
Andrew