I use both methods that Mr. Hanson uses. With the rubber stoppers or PVC, I drill 1/4" holes in the ends, that stops the moisture issue. Also, I take a plastic jug and put a few papertowels in the bottom, stand the barrels with the stoppers and holes in them up in the jug, then every now and then I just put a few drops of oil through the top hole and presto, no worry about rust in the barrels. Also, if your gunsmith likes to ship barrels wrapped in newspaper, do not store them that way, the ink in the newspaper will etch/rust the outside of the barrel. I'm not sure how long it takes but I got in some barrels while I was overseas and the wife put them in the safe still wrapped in newspaper and they looked very rough when I got back (several months). The bores were ok but the outside was pitted very deeply and couldn't be polished out.
Hovis