The internal temperature for smoking/slow cooking is directly controlled by how much water you put in the drip (water) pan above the fire pan.
The more water in the drip pan, the lower the internal temperature will be... the less water... the higher the temp.
The drip pan works just like an indirect heat radiator...
If you remove the drip pan totally, the smoker becomes a grill... too hot to smoke or slow cook.
2 cups of water in the drip pan will put the temp right at 250 deg with a good fire going.
Adjust the amount of water to adjust the temperature... if it starts getting too hot?... add a cup of water... not hot enough? you have too much water in the pan.
Its that easy... yet nowhere have I been able to find anything written about this... so here it is.