define 'when its ready'. i've read that the mylar, or whatever those bags are made of, doesn't allow the wine to age. If you're making something that is drinkable right out of the fermenter, i would say go for it, but if it were something that would normally need a few months of bottle aging, it may not come out as good. I couldn't say anything for certain, though. i haven't tried.
if you do go ahead and use the box, be sure to post the methods and results here. I'm curious to see how it turns out, my in-laws are big into the francia boxed stuff.