That pack should serve you well. I followed the same install path and sandwiched the pack as you outlined. As for preferred placement, I used several cardboard templates and moved them around until I found the correct spot. So, a lot of trial and error. One thing to consider when moving the pack fore and aft, make sure you take seat removal into consideration. I mounted mine very close and low to the rear of my Ultimate King and almost made it impossible to remove the seat. Another 1/4" forward and I would need to remove the pack to remove the seat.
If you also have the pack lights, use a weatherproof quick disconnect to supply power.
Let me know if you have any other questions and I can try to provide further insight.
**Edit: Too late, looks like you are already there. lol