Scott,
First, welcome to the site.
Now to the question at hand. I have a GOSM that is very similar to your smoker. I use large chunks (2" cubed to fist size) of whatever type of wood I'm smoking with. I usually put two chunks in for the first part of the smoke and add the meat when the thick white billowing smoke stops. What you're looking for is a thin blue smoke (TBS). The white stuff is impurities and steam (if you soak) burning off and can become creosote and leave a very bad bitter taste. Ok, so now that the wood has smoked down to invisible or less smoke (usually about 45 mins to an hour and a half or so), I top off the water pan with hot water, and toss another chunk or two in. If the original chunks are white ash then they are pretty much done, if they are still black coal looking, they are still imparting good smoke. I repeat this cycle until my meat hits 140* or there abouts. Some will smoke the duration of the cook, but there is an argument that most meat stops absorbing smoke at around 140. Once at 140, I continue to top the water off every hour or so until the meat is at the desired pulling temp.
Hope this helps you out.
KE