I have a
Masterbuilt 2-door vertical propane smoker and I'm also have a heck of a time maintaining even temps (e.g., 225). I've modified my smoker by adding door gaskets, skirts around the base to protect against the flame blowing out, a cast iron pan for wood chips, the Bayou regulator and I even blocked about 1/3 of the holes in the burner with small brass screws as others have suggested. I've had this smoker for about a year now, and I have a very difficult time maintaining anything close to a stable temp. The mods I made have pretty much eliminated the flame-outs; I think the skirting and especially plugging the burner holes were most helpful.
About the best I can do is slow the rate at which temps ping-pong up and down. Rarely can I go more than 30-45 minutes without adjusting it, and often it requires more frequent fiddling. Like Ted, I am often quite happy with the outcome when I smoke, but this thing requires constant babysitting. I have a decent remote thermometer (a Maverick 732) and were it not for that, I'd have to check the smoker every 15 minutes to make sure it wouldn't be getting too hot or too cool.
I will probably try adding a separate needle valve, even though it seems the Bayou regulator already has one, but I'm also about fed up with this situation. If I ever get another smoker, I think I'm going to shell out enough to get something with a thermostatic control so I run the smoker and still get other stuff done.