Is it the Brinkmann Smoke and Grill? That is the one most commonly bought here in the UK. If so, it is not really a smoker that lends itself to smoking low and slow out of the box and requires some significant mods to make the temperature controllable. If it is the model it has no air real management other than some have a top vent - the air intake is a gap all around the bottom of the fire box. They are really designed for hot smoke roasting and by using the top vent will maintain a temperature of about 160-180 C without too much effort.
Without that air control you cannot sufficiently regulate the smoker internal temperature. If you look online you will see that there are mods that you can make to the smoker to give you more control for the Low and Slow cooking but you have to really ask yourself if it is worth the effort.
The most effective way to progress with your smoking is really to replace your smoker - or more accurately add an additional smoker to the one you already own. For versatility a good quality 57cm kettle BBQ will give you what you are looking for at a very reasonable price. Look on ebay and you can often pick up a second hand Weber for £30-£40 and some of the larger garden centres often sell them off cheap at the end of the season. One of the guys who was at the smoking weekend this weekend picked up a second hand no-name kettle BBQ for £10 and cooked some great pulled pork on it.
Another option is the Callow bullet smoker at about £85. The guy who designed and imports the Callow actually used to sell Brinkmann smokers and so he has designed an entry level smoker that is aimed as a similar price point - but without the Brinkmann limitations.
With
the Kettle BBQ you can obviously grill.
By putting the lit coals at either side of the coal grate and cooking using over the middle using indirect heat you can hot roast - similar to the Brinkmann
By making a snake of unlit coals at one side if the coal grate and letting it slowly smolder you can easily maintain a cooking temperature of about 110 C for 6-8+ hours for your brisket, ribs or pulled pork.
A couple of tips when cooking any meat low and slow...
You only really benefit from the smoke for the first 3 hours or so. After about 3 hours wrap the meat in foil for the remainder of the cook and it will stay moist inside.
At the end of the cooking time leave it to rest in several layers of foil for at least an hour. It will continue to cook and will be very moist when it is cut.