If you have the wheel bearings that you can grease without taking the wheel off it's pretty easy. Use a hydraulic jack, or scissor jack ( read your manual as to where to put the jack) close to the wheel as possible. Put wheel chocks on teh other wheels so the camper doesn't move. Jack it up just so you can spin the wheel. Take the rubber cap off the axle hub, connect a grease gun to the grease fitting, and slowing pump in grease while spinning the wheel. The old grease will start to come out the front. slowly pump the new grease until you see it coming out the front, and your done. Go to the next wheel and repeat. It's a little messy, but easy to do, and you should know how to jack up the trailer anyway, just in case someday you get a flat. There are some videos on the web on how to do it too.
Model X19H Expandable
GMC Sierra Pick up
Been a camper since I was a kid, and that was a long time ago :)
From pup tents with no floors, to tents with floors and flies, to a pop up, to the expandable.