Well, first I have a KA. So the inside is a little different. Second I do not have a roll out cargo cover.
But here are some more Pics that should give you some more to work with.
In this one if you look close you can see I pounded flat the ends of the pipe (see EDIT "pipe end" Pic) which hold the rear of the shelf in place. The pipe ends sit in the small hook that would hold the roll out cargo cover end when it is pulled out. You can also see a small notch I cut out for the top of the cargo cover plastic "hook" (cut into the bottom of the shelf). The pipe is held on with rubber insulated "P" style pipe clamps. In the Pic the pipe has slid down to the ground, so it is not "in the installed location" by the notch.
The forward part is held with a 2x2. The 2x2 sits in the spot a roll out cargo cover would sit when not pulled out.

In this one you can see the U shaped corner cut outs so the sides don't hit the "D" pillar.

The weight of the shelf keeps it in place, and it is so tight fitting I'm not too worried about it moving around. Unless the rig rolled over, or I was wheeling really hard.
EDITBecause the pipe in the rear is so small (1/2"ID) I used a thick walled pipe. I believe it is 3/32".
Here is a more detailed Pic of the pipe end.
