I do not quite understand you.
Do you want an USD or an offset.
It seems to me that you want an USD.
Basically I think you can attach gravity feed burner to USD.
Then you can save vertical space, and may add one more level of grill.
Also by gravity feed burner, you will have better and automatic control of temperature.
If this is true, a gravity feed burner has benefits over cold smoker.
The primary purpose of cold smoker is "COLD SMOKING", fire box is just an added feature.