IMO, the most actual work to manually packing the bearings is jacking the the trailer and setting the jack stands. Everything else is a little tedious but not physically difficult. If you have to jack it up anyway why not pull the hub, clean and inspect the brakes, get eyes on the bearings and races to check for wear or heat discoloration and replace the seals. It's greener, uses less grease. All that extra grease packed into the hub is actually a heat sink that will cause your hub to run hotter and not cool off at fast. Unless you're consistently pulling the trailer through hub deep water you don't need all that grease in the hub.