you could get away with covering over your bearing for paint, it's surprising how often an aerosol lid will fit nicely into a hub, if it's slack run a bit of tape round it so it's a nice snug fit and tap it in with the heel of your hand til it hits the bearing, i do this more for grinding in the immediate vicinity of a bearing but usually will apply a bit of paint for rust proofing and that keeps it clean. a smear of vaseline will also protect your bearings, theres a big hgv trailer repair place not so far from me , they use bags and vaseline to protect the bearings and vaseline to protect their eyebrows....
thinking about it they had an awful lot of vaseline....
