Many people have written up great HOWTOs and / or produced video instructional guides on trailer bearing maintenance. There is nothing special about the ones on Scamps. They have Lippert or Dexter axles and bearing assemblies. I would use Google.com to find them and review them since they will (as a rule) be much more detailed and informative than the brief replies you will get here.
Also the owners manual for your
axle (Dexter or Lippert) should have the process explained.
I would however caution you that some of these online guides are contradictory or just plain wrong in some aspects, so after you review a number of them, ask here to clarify anything you need to.
Buy from NAPA, e-trailer.com.. or 100 other places. Quality varies some but its hard to tell what you are buying anyway.
If you do it.. do both inner and outer. If you need to replace a bearing.. replace the races also (and thats a bit more complicated but also explained online on 100's of online sites).