So I mentioned that I think I mounted my controller in the third best location. I was going to mount it to the right of the steering wheel, but thought I would be bumping it with my knee. I had that problem with this controller in my Explorer. I finally decided on mounting it to the left slightly inside the fuse panel. During my trip I didn't bump it at all.
However, I would like it to be less intrusive. I think that INSIDE the fuse panel with the fuse panel cover on would be the second best location. I noticed that the Tekonsha Voyager is 3"Wx5"Lx1.5"D and the top is flat. That might fit inside. Once the controller is setup you really don't need to access it. I only used the manual knob one time in 10 years, so I don't really think you need to use it for lightweight (<5000Lb) trailers.
Finally, I don't know where the best location would be, still looking!