I soak my wood chips in water for about 30 min., then wrap them up in a packet of aluminum foil. Poke a couple of holes in the foil and put them on the coals. When I threw the chips directly on the coals I would get a high volume of smoke for a few minutes, then nothing. The aluminum foil method gives me a good amount of smoke for a lot longer.
Keep in mind that when you see the thick, white smoke that that is bad and a sign that the fire is burning incorrectly. You want it to be almost non existent, light blue smoke. Thats when the good flavor is happening. In our offset we cook soley with wood, so we are adding a stick every hour or so. In the Weber I usually add 5-8 fist sized chunks of wood at the start of cooking and it gives me all the smoke flavor you could want. Ive never really had any success with wood chips, they just burn too quickly to get any real flavor out of them.
Galvanized metal can be quite toxic when heated. Never use galvanized metal for your homemade firebox. A galvanized smoke stack may be okay but I don't think it would be wise to risk that either. Any other home-made metals should be from a known source as well. Metal has pores and can hold chemicals for years, even after a good cleaning and burning out.
