Nice blind set-up. How many single arms are you using? How do you attach your umbrella to the single arms?

I using two single arms, one of them attach to the umbrella wia Manfrotto Car windo pod, other arm is attached to the handle of the umbrella. To able to do this I reshaped the bottom of the umbrella plastic handle in order to fit into the hole on the camera platform on the single arm which was designed to hold photo umbrellas I think.
For better understanding here are a few picture wich shows how I did attach the umbrealla to the single arms and the single arms to the Wimberley tripod head.
The pictures shows the setup with my Pentax camera with a 170-500m lens, but I use this blind with a Nikon F6 and Sigma 300-800. With the Sigma 300-800 lens the camera get more farther away from the tripod head so the single arms are not in my way.

So here is the upper attachment point with a windo pod:

And this is the bottom attachment point. With the side thumb bolt (shown by red arrow) I can secure the reshaped bottom of the handle into the single arm. But without tightening the bolt it still remains in it anyway.

And here you can see how I attach the single arms to the wimberley:

There is a much more rigid arm from Manfrotto which can do the job better, and even may one arm would be enough! But that is more expensive, and I can use this arms for holding remote flash too, so I choose this one because it make my gear more flexible.
I using them for close up photography holding speedlights as they was designed for.