Put it in the groundMan, if you could find a way to easily get it in and out of a whole in the ground, you could hold on to even more heat for those really long smokes. It would solve the "yard waste" issue as well.
One of two things is happening,
1 You light to many coals, but I kinda don't think so since you didn't say it ever came down.
2 Which is my guess, you have air leaking in letting the fire build to big.
Most of us only light 1 briquette per ten lbs or so then dump them on top.
I love the idea of making one of these but how do you attach the ball valves on the bottom?
A simple pipe nipple and a couple EMT conduit jam nuts works pretty good if you use 3/4 nipple threaded in a 1" hole and the jam nuts to lock it down good.
A bunch of people have just used the thread the nipple in the 1" hole with no jam nuts and not had any problems.
A few have also just drilled there holes and used frig magnets to cover or partially cover the vent holes with good success. This way would drastically cut down on the build price.