I found this info on www.cbbqa.com
. Hope this helps.
7.2.1 Modifying charcoal-burning bullet water-type smokers
The smoker modification Section was edited by Tom Kelly from a summary of posts by Mike Roberts, Pat Lehnherr, Harry Jiles and The Bear--
The Brinkmann water smoker is an inexpensive tool which can make some excellent barbecue. It is sometimes referred to as an ECB on this mail List (El Cheapo Brinkmann). Don't let this moniker fool you however. The ECB makes some mighty fine barbecue right out of the box. However, there are several modifications which can improve its performance, ease its use and therefore enhance your enjoyment.
Modification 1 - Improve accessibility to the firepan.
WHY? - The small door on the side of the Brinkmann does not allow for easy access to the firepan. Adding wood, lump charcoal or briquettes is a hit or miss prospect. Try throwing in a few preburned Kingsford briquettes and you'll see what we mean. This modification makes fire maintenance a snap.
HOW? - Remove the legs from the unit and install them on the outside. Obtain a length of ungalvanized threaded rod and six matching nuts. Alternately, obtain 3 bolts of sufficient length and 6 matching nuts. Drill through the lip of the firepan at three locations approximately 120 degrees apart. Center the hole between the inside and outside diameter of the lip making sure that the nuts can be installed without interfering with the pan. Measure from the ground up to the ledge on the legs that the firepan used to sit on. Cut three pieces of threaded rod about 1 inch longer than this measurement or use your 3 bolts in an inverted position. Now all you do is thread on a nut above and below the lip of the pan to secure it in place at the same height it used to sit. Set the Brinkmann smoker over the pan and you are ready to smoke.
Starting a fire and maintaining it is now much easier. When you have to add fuel or ‘shake up' the fire or remove ash, all you have to do is CAREFULLY lift the unit straight up about 6 inches and set it aside. You have to be particularly careful if you have water in your water pan. Tend to the fire and then replace the main unit. The top is never removed and the door is not opened so less heat is lost.
Modification 2 - Improve firepan airflow
WHY? - The Brinkmann firepan has no air holes to improve combustion of the fuel. It apparently used to but rumor has it that someone used the smoker on a deck and some hot embers dropped out and set the deck on fire. Ergo, no more holes. But, no holes means poor combustion and incomplete burning. This modification lets more air get to the fire.
HOW? - Take the firepan and drill about five 3/8-inch holes in the bottom of the pan. This will give you about 1/2 square inches of airflow area. This increased airflow allows for better combustion.
Another advantage of this modification (assuming you have made modification number 1) is that you can lift off the main unit and using fire gloves or a couple pairs of pliers, pick up the firepan and shake it. This gets rid of much of the ash and keeps the holes free for air supply.
CAUTION - DO NOT USE THIS MODIFIED UNIT ON ANY COMBUSTIBLE SURFACE (Such as a wood deck). If you plan on using this on a deck, make sure that the unit is placed in a sand-filled tray or similar fire resistant arrangement.
Modification 3 - Improve accessibility to the water pan
WHY? - The small door on the side of the Brinkmann does not lend itself to easily refilling the water pan. Adding water is a hit or miss prospect and can end up with water spilling into the firepan.
HOW? - Technically this is not a mod but more of a tip. Run down to your local K-Mart or auto parts store and purchase a plastic funnel with a long flexible filling end. Then, adding water is a snap. Open the door, hold the funnel end over the pan and fill with water safely from the other end.
CAUTION - ADD WATER CAREFULLY! IF THE WATER HAS COMPLETELY BOILED OFF, ADD WATER VERY SLOWLY TO AVOID BEING BURNED. THE WATER CAN FLASH TO STEAM OR BOIL VIGOROUSLY IF ADDED TO A VERY HOT, DRY WATER PAN.
Modification 4 - Improve temperature indication
WHY? - The temperature gauge that comes as standard equipment with the Brinkmann leaves a bit to be desired. The ‘LOW, IDEAL, HIGH' indication doesn't really tell you what's going on temperature wise. You'll be hard pressed to maintain 220F using the stock gauge.
HOW? - Obtain a good quality candy or meat thermometer (temperature range about 150-350F) that has a shaft at least 4 inches long. Obtain two matching corks, each about 4 times the diameter of the thermometer shaft. Drill a hole through the center of one of the corks (top to bottom) just slightly smaller than the shaft diameter. Now drill two holes, one in the side of the dome and one in the side of the body. The hole should be sized so you can push the cork in about half its height. The holes should put the shaft within an inch of the upper surface of each grill. Now you can monitor the temperature at the grills more accurately. Plug the unused hole with the undrilled cork.
NOTE - Don't try to use the existing hole where the stock 'thermometer' is installed. For one thing, it's too large to easily get a good fitting cork. For another, it's several inches above the upper grill and that location will read somewhat hotter than the grill level itself.
A more expensive but easier fix is to obtain a Sunbeam or Polder electronic remote reading thermometer. They can be purchased for around $25 to $30 at kitchen shops or stores such as Service Merchandise. Push the probe through a small piece of wood or a cork so that it is not in direct contact with the metal grill, replace the lid and you can read the temperature at the remote display. Very accurate.
Here is some more info from the same site
I purchased a Brinkmann charcoal water smoker last year. I'm having some problems with temperature control. The temperature drops as the hours go by even though I have the same size fire. Any ideas on this?]
When you light a big pot of charcoal, with the smoker top portion off, there's plenty of oxygen available. All the coals get burning; all the coals get hot; all the coals give off a lot of heat. [Editor--the same applies when you start a fire in a bullet water smoker where the fire pan section cannot be removed from the smoker section.]
When the smoker top gets put in place (or the fire door closed), the air flow gets cut back quite a bit. The coals slow their burning rate, and they don't generate as much heat. The overall amount of heat being transferred into the smoke chamber is less. As the charcoal burns, ash accumulates, further reducing airflow. The only solution I've found that works well is to lift the entire smoker off of the firepit (my smoker is actually three parts: fire pit, cylinder, and dome top) and then use a shovel to dump the burning charcoal on top of a grate (getting rid of ash, which is also removed from the firepit) and then reloading the firepit with the burning charcoal and more that is already burning. Because of the lack of airflow, adding non-burning charcoal to the pit doesn't do much good.