Aussiedistiller, Home Distilling, Moonshine, Home Brew

The humidity and temp play a part in evaporation rates and the contents of a barrel will want to stabilise at about 75%. As at75% the water and alcohol travel through the wood at the same rate.
Sounds like thirsty angels and part of the reason most people go for larger barrels.

You would not loose booze if you stored on ss beer kegs with dominoes in it for oaking

Mate of mine just started using barrels, lucky for him, his wife bought him these barrels. She also did all the research on/about and how to get the best out of these barrels; one point I found interesting is that, when it's humid (raining, etc) water tends to evaporate more than alcohol... so it is possible for the ABV to increase.
I don't know if it happens often, it's certainly the first time I've heard about it.

I have heard of gaining ABV while aging in a barrel, just couldn't remember the circumstances how to do it, I know the guy who bottles Heartwood single malt whisky does this with some of his releases.