Well, I've begun working on my jack mount for my Prinsu rack. Started with this:

just got these (7075 aluminum, 1/2: thick):

next is to add a small piece of angle on the back side (to the holes above the notch) and then that will bolt down on top of a cross bar, and the holes to the sides of the notch will bolt to the rack frame.
these sit on top of the cross bar, and are bolted to the rack frame and to the cross bar itself.
a bolt will be added to the section above the large cut out to hold the jack.
then it will be painted (plastic-dip) black.

just got these (7075 aluminum, 1/2: thick):

next is to add a small piece of angle on the back side (to the holes above the notch) and then that will bolt down on top of a cross bar, and the holes to the sides of the notch will bolt to the rack frame.
these sit on top of the cross bar, and are bolted to the rack frame and to the cross bar itself.
a bolt will be added to the section above the large cut out to hold the jack.
then it will be painted (plastic-dip) black.