I have learned over the years that the best way to package a Barleywine is to bottle condition it. Of course, if you can tie up a keg for over a year than I suppose that would work as well. I have tried a beer gun and counter flow, but bottle conditioning has worked best. I recently did vertical tasting of my Barleywines (1-5 years old) with my Homebrew Club and the overwhelming favorite was the 5 year old.
We have a good supply of kegs, and aging different beers is part of our normal practice. I like the flexibility kegs offer, being able to easily pull a sample now and then, and comparing this month's flavor profile to last month's flavor.
I have a 2.5 gallon keg also, that is great for aging smaller size batches, or a split brew.
Our Barleywine just turned one year old now, still in the same keg. I do not bottle beer, except to give away and for competitions.
This brings up a question. Why would aging beer be better in a glass bottle than in a stainless steel keg? Has anyone done side-by-side blind taste tests? I bet someone has!
And how about cask-conditioning, or simply keg-conditioning?
Well-brewed kegged beers can store well, usually at relatively cold temperatures (around 4°C [40°F], the average temperature for normal storage of non-pasteurized kegged beer), for 10 years or more.