Panda (Classic) Making the panda mighty again

We've had 'The Mighty Panda' for nearly 4 years, it's been a workhorse during a long house renovation, moving materials, livestock and timber around but we've known that the sills were very rusty for most of that time. Anyway having removed the carpet yesterday the extent was far worse than expected..

I've started this thread to show the damage and repair as well as ask lots of questions of you far more knowledgeable folk. Here are a couple of pics (I hope..!)