What is this fiberglass piece behind the front fenders on a 11 Ram Sport 4x4 Quad Cab 1500

Doing some research , seems to be an area for rust

And it's not coming off , it's rock hard , and I was told if I tried to remove it the fender would come with it ?

Anyways enjoy the pictures

And how can I treat that rust spot before it bleeds through

Truck is mint , 26,000 miles , and now I see this

If it bleeds through , I would be replacing fenders , also was told the new fenders have this fiberglass tape pre attached already

It's a moisture collector plain and simple