thats what done it for me on my estate mate

there is an inner sill, then the floor pan, plus another bit that goes in the middle before the outer sill

and this was all rotten on mine and after a month welding it up a few years ago with fresh metal it only lasted another 5 or 6 years before it was back to the same condition again and i just couldn't be arsed to put so much work back into it

hopefully the bodyshop will be able to fix it better than i could as they will spray it with stuff and keep it inside, not like mine in the garden in all weathers

don't give up hope