Bob - you're probably not going to find the "sweet spot" with the smoker empty. When you have a meat load in there, and a water pan (even if it's filled with sand), you'll be able to dial it in. The meat and water pan add mass to stabilize the temp. With the box empty, there's nothing to absorb the heat, so you'll see big temp swings.
I'm cooking a 8.75 lb butt now, and I posted (in the pork section) that I'm only seeing a +/- 5-degree swing in set temp in my #1. Try your sweet spot experiment when you have the smoker loaded. Also, 4 hours for the seasoning is plenty. All you're trying to do is coat the internals with creosote to remove the "machine oil and stainless steel" smell. You're first smoke will continue that process.
Good luck!