i want to put bedliner in the back hatch area of my explorer, i removed the carpet and the 4 chain things, but under neath the carpet is this large patch thingy, i dont really know how to describe it, its like a huge sticker, if i try to scrape it off with a putty knife it breaks off kinda like half hardened clay. Shold i continue removing this or should i leave it and put bed liner over it?