Congrats on the new smoker, is it a "new" model, what I mean is, is the wood box heavy cast iron with slanting sides, are there slots in the cover?
If so I think you will find it best to leave the cover on, fill it with chunks the size of your fist and include a few chunks of lump, that is what I do and can go ten hours TBS on one box. I have found split chunks work better than round branches and I place the split side next to the floor and walls of the box. I close the top vent to about 3/4" to keep the heat in, I found that as the air was rushing through the wood burned too quickly and caused flare ups, I figured since there is not alot of heat rolling out of my oven, why not try the same thing with the GOSM? ...Works for me.