Bearings and grease.
I have been using bearings, drums and brake assemblies from etrailer. The bearing kit from them is about $19. The bearing kit from the Lippert website is $31. Doubt the bearings are different from the two locations. One thought was to replace all bearings and cups on all four wheels with higher end components, like timken or such. I have tried replacing just the bearing before since the cup looked fine, but have also replaced the whole thing when the bearing did not solve the issue.
The grease I have been using since the start is Valvoline DuraBlend, a sythetic blend grease. Drop point of 500 F. I have greased by hand and by using a bearing greaser (double cone with zerk fitting type). I have greased bearings before, I know to really work the grease in to the bearing until it starts squeezing out from the sides, then pack the sides with grease. I slather grease around on the inside portion of the hub between where the two bearings ride. Every time they have failed, there has been grease in the hubs and remnants of the bearing. I have even traveled with the grease gun and added several shots to each during trips. They do not get cooler. And the two failures I had were the outside smaller bearing, the inner was still working or semi working I guess.
