I went out and took some pictures. We'll see if they are any help. I posted a thread on an "ashtray mod" I did a while back that totally replaced the stock rack and firebox. It worked well. (http://www.smokingmeatforums.com/for...ht=ashtray+mod
) I was proud of it but didn't get any feedback. Oh well.
The gap between the rails is 12" for your water pan. The stock pan has 1 1/8" inch lip on it (all the way around) to keep it on the rails.http://i305.photobucket.com/albums/n...t/gosmpic3.jpg
The rack for the firebox raises the box 2 " off the floor of the smoker. I actually cut my legs some-can't remember how much I took off. I was told by another member that the rack was too high.http://i305.photobucket.com/albums/n...t/gosmpic4.jpg
I don't know why my pictures don't show without clicking on the link but I hope they help. The stock firebox is too heavy and a 9X13 cake pan works even better. Instead of the rack you could probably support it with bricks under the lip. Many people put bricks in the bottom as an added thermal regulator. You can see where my bricks sit and if laid down they would keep the pan close enough to the burner. By the way consider the needle valve mod. It really helps with minor temp tweaking. I don't have that link copied, just do a search.
The unit is a good one and I've had lots of success with it. Enjoy.