In a horrible place to weld

It the top near the top join. I've replayed the boot and mine only a 5 seater

Rust. I was thinking cutting the rust strip out and multiple layers of grp and covering the whole wheel arch to protect it

I have a 300dti. My wheel arches are starting to sign of rot( normal). I work a lot with grp and fibre based products with work. Is it possible to line the wheel arches with one of these product and still pass an mot?