I assume you are talking about the Masterbuilt cold smoker?
I have used it, I actually like the results very much. First you do not need to attach it with the wingnut and screw. Which I would guess you already know is a total pain in the butt.
I use it as a warm smoker, we never even got a freeze here last winter. So I smoke warm.
You referenced the set and turn off. What I do is, well lets talk preceedure first. I don't know what others do, but this is how I do it.
I preheat my smoker to 275 which is really about 230 on my smoker. I always prehest to max temp to smoke, why? Because when you open a door to insert a meat you lose chamber heat which is slow to be reclaimed. IT heats the chamber as hot as possible and I think it helps. Also nearly all things "cold smoked" are brined /cured. I find they need a dewater cycle for 45 mins to an hour on high temp to dry it, and since it doesn't hurt anything I just do it all the time to kick anything I am smoking in the butt to get it warm faster.
There is the continuing debate as to when meat takes the most smoke. My personal belief as to what I have always seen was sung out here at one time as from 90 to 140 IT the meat's pores are the most open. Made sense as I know heat causes any substance to become less dense. So I can see where that would allow more room for the smoke to infiltrate the meat. At a certain point the pores become saturated. Now you can still take some before 90 and after 140 but at a lesser rate. The prime smoking temp is from 90 to 140 from my experience and that will be discussed and cussed I am sure. Its my opinion and I am sticking to it. Why do you think you need to smoke so much when cold smoking where as warm smoking is at a much faster absorption rate.
With all this said. You must have a draft thru the unit. I don't smoke during the dewater cycle and it usually works out about right as ti the temp level needed to apply the bast smoke. Usually the IT will be around 65 to 85 after the one hour dewater no smoke cycle. This is when the door is cracked, the top vent fully open getting all that water out.
At the very end of this is when I kick in the aux smoker and close the door. I have used chips which I know not why worked better damp. But normally I use pecan shells in the chimney. Once its up and smoking, crack open the ash tray. It will take 30 mins or so to see the MES40 fill up with smoke slowly from the bottom to the top. Its really cool. At that point is when I really regulate that discharge vent little adjustments till its smooth were you want it. I had to play around for a few smokes paying attention to get it where I understood my smoker.
Now is when I drop the temp to around 120 to 180 degrees which will very very slowly raise the meat temp. I have adjusted the vent to approx. 1/2 closed also. I want to maintain a draft but not lose all my smoke, it has to settle into a continuiously metered flow. Now I turn my aux smoker off.
It will smolder supplying a small amount of smoke. You MUST leave the door closed or you'll lose the draft.
At this point, I will bring out another discussion topic. remember this is all from my experiences. I got my first electric analog with no instruction and a bed of dead charcoal in the bottom in the early 80's, I have worn the bottom out of three of them and there was no vent and no holes. The chamber filled with smoke, the oxygen depleted, the chips smolder till they have to go out due to no oxygen. You Never open the door, Cook it till done then pull it and I'll match color and taste to any other smokers. You can smoke without fresh air and its not hard. Its just hard to let go and try when you've seen firebreathers all your life.
But With your MES40, and the Masterbuilt cold smoke attachment, I really have no problems with the smoke after its lit. And if I do, cause it does take some study to understand the air flow, just click the cold smoker back on. Don't be affraid, You really can't hurt anything. It just takes a bit of practice.
Remember everyone has a different way, I don't say mine is the only way, I don't say it will work for everyone else, I will say I have practiced, and watched, and learned and it will generally work for me. I have used pellet trays, the adjustable oval pellet burner, I think there should be enough smoking done to have room for everyone. You just have to learn what best suits your style with that meat at that time. Its all fun, and good to eat.
EDIT: I just noticed you are using a MES30, I usually used the chip tray or a pellet smoker with my MES30. I don't know it won't work as above stated, but I have never tryed it in the MES30.