Anyone use this? http://www.stainlessbrewing.com/Dry-Hopper_p_155.html It looks like it would take up a lot of room in the keg. It looks interesting, but it seems like you would only be able to dry hop 4-4.5 gallons of beer at a time in the keg.
I haven't used one, and I'm not sure how that would jive with the dip tube on some of my kegs, but it looks like it might make a good hop basket for a boil kettle so long as the kettle was tall enough.
Check this out instead. Even if you need two of these, you will still come out a lot cheaper. http://www.amazon.com/Extra-Large-Jumbo-Size-Twist-Lock-Infuser-Stainless/dp/B004X4LGIO
I was looking at that thing, it wouldn't take up much space, the whole thing is just mesh. I'd just make sure the lid has a way for air to escape as the keg is filled to make sure there isn't a pocket of air inside that can't be purged with CO2.