Thanks for the info and details post.
With my WM Drum i have basically done the same thing as you. I used the open end as the top of the fire basket but i made the top wider by cutting the top lip off, but as you said using that end as the bottom would have been a lot better and much easier.
I've only used my UDS around 5 times and struggled with temps every time but i have a feeling this is due to the WM drum not getting as much airflow as it needs so i may have to work some magic to make it more efficient.