I have one similar, I don***8217;t use the firebox unless smoking something big like a brisket. I usually make a charcoal fire on the side nearest the fire box (cause that***8217;s where the vent is) place a pan full of water on the other side. Put your meat over the water and drop some soaked wood chips on top of the well lit charcoal.
Open your vent bout a 1/4 of the way. If it gets to hot close the vent some, if fire is going out open the vent more. Add wood chips periodically to keep it smoking, add charcoal if the fire is looking wimpy.
On the left you can see pan full of water under the meat, on the right you can see I just added some charcoal to extend my fires life, after the new charcoal is well lit I will throw some soaked wood chips on top to get the smoke going again.