Controlling temp on Dyna Glo LP smoker

[Nicely67]

I have a Dyna-Glo 36" vertical LP smoker. My problem is figuring how to control the temperature. With the burner on low, the top chimney fully open and the bottom vents each open about 1/2"", the temp climbs to over 275. My only alternative is to turn the burner off for about 20 mins until the temp is down to 200 then turn back on low for another 30 mins. I have to keep repeating this throughout the smoking time.