I use a gravity feed smoker. Built my own actually - I've posted pics on here before of it. Its roughly a clone of a Stumps smoker with my own design twists. It has a firebrick lined furnace area (inside 1/2" steel). Thing probably weighs 800lbs.
I can (could) cook 8 briskets or 20 pork butts on it comfortably if I wanted to. But the cool thing is it uses so little fuel I don't feel bad about throwing a couple racks of ribs on it or only a couple pork butts. Being fully insulated it's very efficient.
With something like a DigiQ and a fan you can definitely leave it unattended for extended periods of time and cook at a pretty constant temp. On a single stack/load of fuel I can get 8-12 hours (depending on fuel type and temp, etc). I can do a rib only cook with half a bag of charcoal or so.
I've used it with brick charcoal + chunks of wood as well as lump charcoal - great results with either, just depends on how much smoke taste you want, etc.
Finished with epoxy primer and single stage urethane (car paint):

Cutaway view of the sketchup model I made showing how it all goes together. Air flows from the fan blowing below the furnace area (through the ash box) into the furnace then out into the bottom of the cook chamber then out the top/side exhaust. Deflectors at the bottom keep the temps equalized left/right and front/back.
It's called gravity feed because the feed chute is filled with fuel but ends up being starved of o2 so it doesn't all burn up at once. The fire burns only within the furnace area (in my case lined with firebrick) and as the fuel turns to ash new fuel drops down into the burn zone.

The furnace area before the feed chute and exhaust vent was welded on. I made it such that the firebricks could be replaced from below through the ash box if/when needed.

Fuel stack, furnace, ash box, and exhaust vent welded together:

The guts assembled, before insulation, etc:

Closeup of diffusion panel and drip pan:

And then the whole cook chamber:

Everything was insulated before being buttoned up:

And the doors are all sealed:

Air intake:

Ash pan and removeable grill that holds the fuel from falling through until its burned up (sketchup view):

Hopefully that gives you a good idea of how these work.
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