After reading this thread.
The sad thing is that is a known problem with Pitmaker BBQ vaults and safes. The whole build a small fire and keep adding to it is not the answer.
Since the door and firebox door is airtight, there can be only 2 problems. The exhaust is not sealing or worse the intake. Anytime your using a force draft system, to properly tune it, the intake and exhaust has to be easily sealable from 100-0%. I have dealt with many algorithm systems including pellets where you have to control fuel feed which even has more variables. The answer for these BBQ vaults and safes are the exhaust needs to be closed to 25% to keep it from drafting and having the runaway temps. Since your using so little fuel and using a forced air draft system, it's gonna flow 10cfms no matter what the exhaust flow is and actually you could probably go lower than 25%. The intake should be 100% open so the draft has has the ability to use the whole tuning spectrum with the airflow from 0-100%.
This even stems back to drag racing days. You take a naturally aspirated engine with decent heads that flow 350 Cfm @28" water on a flow bench intake and 225 Cfm exhaust, then engine is only gonna make the hp allowed by those flow numbers. Now put a supercharger or turbo on it (BBQ guru or stoker) and now your flow numbers of the heads drastically increased to double if boosted to 1 atmosphere (14.7 psi) the thing is that I can believe Pitmaker hasn't figured out this simple task yet!! What even amazes me more is that when Pitmaker allows people to have problems with their product and blame the performance issues on the customer. A fire runs just like a gasoline engine, wide open all the time until you control it via air and fuel and butterflies (intake and exhaust)
I sternly believe that Pitmaker is the best built cabinet smoker in the world, but when I order mine, it will be made how I want it, and I guarantee it will work how I want it to, perfect, just like my UDS does.