Damn bro, you have the same one I have. Brinkmann Trailmaster Limited right? I would recommend about 3 or 4 good sized chunks, that should last for about a 3 to 4 hour smoke. I will add some pics of my fire box set up, so if you like the way it is, you can set it up the same way. All I know is that it works.
Here is my set up for my fire box
One the lower layer of grates I opted to layer it with fire bricks to hold heat so your fire does not have to be so big.