bratrules, I have a GOSM BB with the needle valve installed and can go as low as 180° and it will keep this temp indefinitely without the flame extinguishing, you didn't tell us what kind of smoker you have, but look and see if the burner air intake area is protected like on my GOSM, it is only open in the front. If it is, make sure the opening is downwind, it is also a good idea, whether or not you use a needle valve, to keep the smoker protected from the wind by using windbreaks as much as possible.
You might want to file a groove on the top of the 1/4" nipple and then start out with the smoker regulator on "high" or fully opened and the needle valve fully opened, then start closing the needle valve slowly until the flame goes out, close the regulator on the propane tank and then make a mark with a felt marker on the knob adjacent to the groove you made on the top of the 1/4" nipple, continue doing this about 3-4 times to make certain this is the extinguish point of the burner and then open the valve about a 1/16 of an inch and light the burner and see if it will burn without going out, if it continues to burn then file a groove on the knob adjacent to the groove on the nipple, this will become a reference for you as to where the stopping point is for the needle valve, just remember this reference is only for the fully open position on the smoker valve, ...then you will find how low of a temperature you can smoke at.
I only use the needle valve in this position for low temp smokes, the rest of my smokes I use the regulator on my GOSM, high, med, low and then fine tune starting with the needle valve fully open and closing it a little to attain my desired smoking temps.
You also want to make certain the air mixture is correct with the needle valve installed, if is is you will have a blue flame with very little if any orange on the tip, if it is a new smoker you should be alright, the usual problem is grease drips down and clogs the air mixture screen, if this has happened your flame will be mostly orange with very little blue.
Do you have a thermometer that you can set for 5° below the flame out temp that will sound an alarm when it is reached, that is how I monitor my low temp smokes, if there is a flame out the temp drops very fast and you will know to turn off the gas and readjust your needle valve, but like I said I have never had a flame out problem after I "dialed in" my needle valve, it's just something you will have to learn about your smoker.
Be safe, have fun and looking forward to some Q-view.