I built my roof rack a long time ago out of 1" square tube. I also have a thread about it on here. We have had the jack for a long time, I just never got around to mounting it. I went to lowes and got 2 1/2 hex bolts and matching nylon lock nuts. Drilled holes in my upper rack bar and drilled some holes in 1" square as offset spacers, then mounted it. pretty simple. Gotta lock it somehow...

 

im probably going to steal that idea

 

I have mine mounted to my stock roof rack like this.