Before I got my smoker, I did ribs on the 22.5" Weber. I was able to hold a temp of 250 for 8 hours without adding additional fuel. Of course you don't need 8 hours for ribs, but the point is you can do ribs on the kettle. Here is how you do it.
If you have a "one touch" kettle, then you will have a hard time knowing how much your vents are open. Before you get started, take a permanent marker and mark the positions for 100% open, 75% open, 50% open, 25% open and 0% open.
Purchase 3 firebricks. It should not cost more than 10 dollars. Set up two of them on edge about a third of the way across. The big side will be the indirect side where you will place your meat; the other side is where you will place the coals.
On the small side, line up the charcoal around the edge three briquettes wide
like this. Make a pyramid by adding two more layers, the second one should be two briquettes wide and the top one just 1 briquette.
Now light just 5 briquettes by placing a large tin can inside your chimney. When those five briquettes are ashed over, place them at one end of your line of charcoal. Place wood chunks on top of the briquettes about every three inches. This pyramid will burn around like dominos in slow motion. Add the third firebrick above the charcoal as a heat sink. Some people use a water pan above the coals in their kettle, but you can't get a very big pan above the coals and you will get a temp spike when the water runs out. The firebrick works much better as a heat sink.
It will take about 20 minutes to get up to temp. Place your meat on right away, and when the temp gets to 200 close the vent down to 25%. You may have to shut down the bottom vent completely to run at 250.
Avoid opening the lid more than once every couple of hours, because you will give too much oxygen to the coals if you do.
If you have any attachments that fit onto the edge of your kettle, take them off when you want to do ribs or other long smoking at low temps, because your lid will fit tighter without them.