Trunk extension problem

I picked up a 70 Chevelle that the person before me installed a new quarter and trunk floor. Strange thing is, on the side where they installed the new quarter, they never put in the trunk floor extension that attaches to the quarter and trunk floor. So now when you open the trunk, you can look in the corner right to the ground. The quarter also moves a little because there is no support.

Im going to have this fixed at a body shop, but for now want to secure the quarter. What kind of metal would be best to fab up for this? Can I just cut something out and temporarily attach it, using a sealer of some sort that will come out without damaging the quarter or trunk floor.

I dont want to leave this the way it is, because Im afraid it will damage the quarter over time. Not to mention it's throwing rocks and other crud inside the trunk. I can try and get a pic if this helps...Thanks, Jason