Instructions to install wheel well trim on a 1972 Ambassador?

[marinero]

Similar to many other posts, I had a tire shred and destroy part of the aluminum skin above the tire and the adjacent under belly wrap. The flailing tread tore off a jagged 1" to 2" strip of aluminum approximately 18" to 20" long. I purchased the subsequent model style wheel well trim from Inland RV which is higher to allow me to cut away the damaged metal. My primary question is, can anyone point me to instructions for installing the sandwich style trim? Before I start cutting and riveting I would very much appreciate some knowledgeable guidance. A few of my many detail questions include:

1. The wheel well exterior bottom edge is not connected to the side of the RV. Does the bottom edge of the plastic wheel well get riveted into the sandwich of trim (exterior and interior) with skin in the middle?

2. What is the best way to determine how much skin to cut off around the well to fit the two piece trim?

3. The skin above the wheel well is a bit floppy as it is a long distance (double wheel well) without attaching to a structural part. How can I best reinforce the the trim and skin? Is there a hard point in the middle I am missing? Or should I (my current plan) add a stiff aluminum stringer along the interior rivet seam?

Thank you!