these are the temp gages I picked up. by having 3, one on the fire box, 2 in the grill area, I can watch and track the temp at the hot zone transition from the fire box (indirect heat) to the gill area (direct heat) and then using the vents raise or lower the heat but controlling the air. I can see what the heat is doing at grill level as apposed to some high point near the top of the lid.
this is the temp gages I use, they are good quality and accurate....
http://www.amazon.com/gp/product/B000XEBFHA
for the venting duct stuff......if you really dont have a smoker....its not going to do anything for you. Because my Char-Griller is a smoker that also happend to grill really really well, I use it to keep the smoke at grill level more, instead of collecting at the top of the lid where the stack starts. The theory is to bring the smoke down and thus thru the meat at grill level, thus exposing the meat to more active smoke. Smoke like heat rises, so instead of rising to the top of the lid and then makign a quick exit, I force it down to grill level before it exits.
The side fire box is basically for smoking. Smoking is slow and low, so indirect heat in the 225-240 range for several hours. Having the box on the side allows you to maintain indirect heat and adds to ease of reloading the coals/wood without openign the main chamber and letign all the heat and smoke out. Convection moves the heat amd smoke from the fire box thru the main chamber and then out the vent. Its the difference between grilling, which is over hot coals, high heat, which sears the outside of the meat to trap the moisture in, and indirect heat which sort of soaks the meat in heat and smoke.
I highly suggest if you want to really get into smoking, get a unit like my Char-Griller. My whole setup was less than 250$ at Lowes IIRC. My grill cooks as good or better than my dads $800 Cajun Grill or his ancient Oklahoma Joes unit. Also.....GET RID of the GAS! lol.....sorry I had to dig a little there.
about covers.....the Chiefs?.....ugg no thanks, I'll take a big ol' Dallas Star on mine but due to the wind here my cover lasted about a month before gettign torn up in the wind