Reloading the charcoal

I'm using a Brinkman Grill with a sealed side smoker. KInda small and I only smoke 5-8 lbs of Boston Butt at a time, but the charcoal  burns up, my temp drops and I have to refill with more charcoal, which is a pain in the Butt and also costs me smoke and heat. What am I doing wrong?   Also, I'm a big bark fan, so I cut the butt in 2 flats and smoke them with just oil and a light rub for 2 hours then take em out for a full rub and put em back for several hours. At that point I stop with the hardwood chips, since the smoke flavor is in and I've heard people say that too much smoke can make you queasy when you eat. I'm also concerned about the smoke residue in my ductpipe smoke diverter; it's some nasty stuff to be eating, butt tastes SO good.     

thanks for hearing me out