Does it have to be a Performer cart?
I always admired the Don Marco 18" WSM mod on the Platinum cart, but when I played around with my 18" bullet on a OTS bowl ash buildup and intake control was always a concern to me. I was into Low 'n Slow at the time and long cooks generated too much ash for me to go any further with it.
When I gutted a Performer to build my dual 18" WSM cart, I wanted to keep the clean lines of the frame and wire bottom rack somewhat intact. I was able to secure PVC pipe caps to two sides of the frame and used the shelf frame of a 1000 gasser side table in the center of the frame to hold the other leg of the 2 bullets.
I had the bowls aligned so a vent was in the front for easy control, the pipe caps held the WSM legs securely but easy to remove and replace. It was the perfect working height for me, and it rolled easily across the deck if it started raining on my cooks.
What did you have in mind to secure the WSM to your cart?