With a Pork Butt, temp fluctuations make no difference as long as the Average temp is what you desire. Setting for 225 and the swings are 30° each way? No problem, the average is 225, where you want to be.
The only time big swings do matter is, Cool Smoking Seafood, Sausage or other delicate meats. Setting for 130 to 170 and getting swings up to 200+, can cause problems like overcooking and rendered fat.
With an Offset, dial in your temp using the Fresh air damper to control how much air gets to the burning wood. Once you are happy, LEAVE IT ALONE. Keep the Smoke Chamber closed and when adding wood, put in a stick or two and leave it alone again. Yes there will be highs and lows but it will settle down. Messing with the Air Damper and Exhaust chasing a steady temp will make you Crazy and accomplish nothing...JJ