When cleaning cap-lock guns, I remove the nipple, stick that end of the barrel in a bucket of cold tap water, and pump water into and out of the bore
to clean it. I then remove the barrel, wipe it dry, then using 4 to 5 doubled flannelette patches, I dry the bore, then spray WD40 into the bore until
it runs out the nipple seat, then patch that out, wipe down the barrel, replace the nipple, replace the barrel on the gun & store the rifle muzzle down
so any excess oil from the breech area can drain out. Here, with a humidity of about 50% average, there is no further rust prevention needed. In your
climate, rust preventive requirements might be different.