I always just put a little grease between the axle and sleeve when I installed it, once the grease is in there it's not going to go anywhere.
I wouldn't expect to have to take that thing apart ever again anyways, those bearings will last forever as long as they're greased and moisture doesn't get in there.
If you haven't assembled it yet, I would recommend using the lightest grease you can find for a grease gun. I used heavy duty equipment lithium grease, for construction equipment because my buddy got me a case of it for free. I kinda regret doing it because the grease was so thick it really added a lot of rolling resistance because the grease will constantly be rolling between the axle and carrier when it's turning. After a couple miles of riding it would loosen up to a reasonable level but every time i regreased it the axle would get kinda tight again. It didn't really hurt anything but it's unnecessary drag that would have been easily avoided.