You've pick a good project. When you get done you'll know exactly what your riding on. Which is better than after paying and wondering "I hope they did a good job".
This is your first time doing them? I would jump back a couple steps first.
Get a manual off your manufactures web site for your axle. Should have torque spec's and what type of grease. Axles usually have a label on them somewhere. My label is sort of hidden. Facing forward, right in the middle and on top. (They make you work for it.)
---If you haven't lifted your RV before, make sure your jacking up RV the right way. You don't want to do any damage.
---After you get it apart, you should see tiny numbers on the bearing. Even if you don't have to buy new bearings pick up a spare bearing and cup and grease seal for the "just in case" situation. Bring in the bearing and the manual that you find on-line. I would buy at a place that axles and trailers are their business versus auto part store, usually more knowledge, if you have questions.
---Re-packing bearings are sort of like baking a cake. Everybody does it different way, but end result is about the same.