When we bought the new van it had plastic carpet over a layer of padding. The padding was very wet. I tore it up because I was afraid that mold would begin to grow underneath. What I found was rust. I removed it by sanding and then applying naval jelly. It took some time but worked great.
Afterwards I sprayed everything down with rustoleum. I used the old carpet as a template to cut a new piece as a replacement.
The finished product.
Sometimes people would come outside to keep me company.