Oh mate, thats some nasty rust youve got there.
I only see one pic with it cleaned up though, have you just treated it or have you patched a panel in now? Ideally a new piece of metal could be welded in, or fiberglass it up and fill it
it was treated with rust treatment then fibreglasses with mesh reinforcement, then filled, and painted that entire section of the boot. we were gong to weld a plate in but we never had any plate handy.
not my idea of fun.