I have been dry hopping in kegs exclusively for several years. I have used bags, balls, nylons and have settled on what I think is the cheapest, easiest and most elegant approach which is the Surescreen:
just making sure i understand this....this is the same screen I use at the bottom of my mashtun. I just put it over the tube that goes to the bottom of the keg (like a sleeve) and then put whatever amount of hops I want in the bottom of the keg (no containment at all) and rack the beer on top? If this is correct, what do you do for the space between the screen and keg at the top?
also, I just read that pellet hops tend to clog the screen. I plan on using 3 oz in a 3 gallon keg and I don't have easy access to whole leaf hops.
The Surescreen is tubular, stainless steel screen which is crimped at one end. It is designed to slide over the pickup tube of a Corney Keg. It allows you to add whole hops unrestrained to the keg for dryhopping. It works very good.
It is designed for whole hops:
http://www.northernbrewer.com/shop/mash-boil-screen
Since writing the post about the Surescreen, I have found and purchased another product that I use as well. It is called the Clear Beer Drought System. It replaces the downtube with a stainless steel float which draws beer from the top of the keg. It works well for pellet hops. It also works for the final keg to draw beer from the top of the keg where it clarifies first.
http://www.clearbeerdraughtsystem.com/
Another important tip that I can pass along is to add 1/3 cup of priming sugar (boiled in water) to the keg at the time of dry-hopping. All hops contain some amount of oxygen which will stale your beer prematurely. By adding sugar, you re-activate the yeast to absorb any oxygen in the hops. This was a key factor in improving my hoppy beers. The shelf life of my beers went from 1-2 months to 9+ months.
I learned at Hop Union's Hop School, at dry-hopping with some active fermentation creates favorable flavor compounds that cannot be created without the action of active yeast.
Adding sugar with the dry-hop makes good flavor and keeps your beer fresher longer.
Hope it helps.