I remove mine every year or so (not too anal about it) and haven't had any issues yet.
That's my advise too....folks shouldn't get to carried away on removing the barrel on full stocks so often.
IMO, unless tremendous care is taken each and every time, the average guy is only asking for trouble after a couple of years.
FWIW, I realized sometimes back in the early 1970's that removing the barrel from my first full stock .69 smoothbore was simply not a good idea, so I left it in place for about 10 years without even checking it.
Once I did check it, everything was fine!
I have owned this old smoothie for about 35 plus years now, I would suspect that the barrel has not been removed from the stock more than a dozen times, and 75% of those times was in the first five years of me owning it.
Although I've never done it, Beaverman's suggestion of using Bees Wax sounds like something worthwhile.
I have seen a few older guns that had regular varnish under the barrel and that was always suspected as being a carry over from earlier times....especially those living in the mountains or high desert where you have fairly dramatic temperature changes in day and night.
(When I owned a gun shop in Deming, New Mexico, I guess half of the guns that came into that shop had been varnished....both stocks and barrels and, at times, I have even seen it on the actions, and it was all done deliberately!)
Uncle Russ...