RV wheel bearings are pretty similar to car wheel bearings of old.
I'd suggest using a synthetic grease rated NLGI GC-LB, meaning it meets their highest rating for both wheel bearing and chassis application. Also use new seals. There should be a metal tag on the axle which will give make/model (most likely either Al-Ko or Dexter).
The one thing that is different than cars is that lighter electric brake axles generally do not have self-adjusting electric brakes. Generally, with the axle safely off the ground (jack plus safety stand) and the tire/wheel installed, spin the tire/wheel forward while adjusting the star wheel out until you can't turn the wheel. Then back the star wheel off until you can turn the tire freely, plus about 4 or 5 good bites more on the star wheel...
Unlike manual adjusting drums (really old cars) when properly adjusted you will still hear a skiffing on electric brake axles, which will be the magnet running along the armature surface.
Both Dexter and Al-Ko have very nice downloadable pdf manuals for free.
Under "Service Information" select complete service manual.
And here, just click on "Owner's Manual".
It is worth it to save both to your hard drive.
As far as frequency, I think both say every 6 months, which I think is a little unrealistic. You would probably never have a problem if you adjusted the brakes a couple times a year, and repacked every two years if you use the trailer frequently. Mine sits up, which I think allows condensation to build up and grease to seperate, so I repack every year.
Good luck, and post back if you have any questions. Sorry about the long post.