I have a 5-gal oak barrel that I have been playing with for a while.
For my first effort, I soaked it with hot potassium metabisulfite, rinsed a few times, then dumped a 1.75 of Evan williams in.
The whiskey turned out really nice
But then I put a batch of IPA in that wasn't all that good (but I attribute it to the overabundance of fresh hops that I used).
Anyway, I've since cleaned that sucker out, soaked it in more metabisulfite, and loaded it up with a 3 gallon batch of port.
That stayed in there for 4 months or so (pretty tasty as it turned out), and then I loaded it full of Strong Brown ale and Roselare bugs. I'm planning on letting the brown sit there for 9-12 months and then I will brew a similar batch and keep the funky bugs going.