Most pre-manufactured smokers with verticle cook chambers which have the heat source directly under the cooking grates will have a pan of some sort. The manufacturers generally recommend filling the pan with water (so-called water smokers).
The water helps to disperse the heat a bit more evenly as well as to act as a thermal mass to retain more steady temps. Water will also add to the humidity level in the cooking chamber...the closer the water is to the heat source, the more steam will be generated, thus higher humidy. This can be used to help lessen the chance of meats drying out due to being slightly overcooked...I say slightly, because severely overcooked meats will become dry regardless of the humidity in the cooking chamber, especially if they are lean cuts...this may just make your meat a bit more forgiving. Some members here use sand instead of water for thermal mass, especially in colder weather.
With your smoker, I would think that the mass of the concrete blocks should be an excellent form of thermal mass, and there should be plenty of it to hold steady temps once it has heated up to cooking temp.
The other reasons for using a pan is to catch meat drippings for adding to a covered pan/foil for brasing to finish the meat, and to help prevent flare-ups from grease getting onto the heat source or fire. I wet smoke most of the time, except for during times which I want to form a good crust/bark on the meat. High humidity can slow the formation of bark, or cause it to have a softer consitancy, so you can use that to your advantage, depending on what you like.
Is this what you were needing to know? Hope it helps you out.
Very, very nice smoker, by the way!
Eric
