This Transit County 4x4 was certainly past it's best. There was rust beneath the under seal so in my opinion somebody had deliberately covered over the problem patches to hide them.
The rear inner arches were rusted away where they met the floor so the bottom of the arch and the floor that it joins to had to go.
New panels were made to replace the lower edge of the inner arch and the rusted parts of the floor that it joins to, some examples of these are below
Once I was happy with the fit of all these parts, the welding could begin and they all became one piece.
The entire length of the right hand sill must have had a total of 50mm of metal holding the bottom edges of the inner to the outer sills, making them rather useless as structural members! Below is an example of a hole that was under the drivers side door step. After using just a wire brush I could see right inside the sill!
This is a view of the same panel from the outside, after i cut the outer sill off.
I replaced the inner and outer front sill (both of which were available pre-made), including rebuilding some parts of the door step and the wheel arch (which weren't available pre-made).
For the rear, the inner sills were not available so I had to manufacture them. Fortunately they are fairly flat so this was relatively simple. In order to get the positioning for this panel correct, I cut and lined them up then cut the outer sill off to gain access for welding (this needed replacing anyway so it made sense to make life easier).
The outer panels were then all carefully lined up, trimmed, tacked then butt welded to the bottom edges of the trimmed original panels and spot welded to the inner sill along the bottom.
The same thing was necessary on the rear outer sill including some reshaping to allow for the rear arch.
This is what it looked like after a bit of clean up and some zinc primer
Obviously a lot of steps aren't shown in full detail here, in part due to the fact that if I'm taking pictures then I'm not welding or shaping metal and partly because the lens on my phone became rather scratched so the photos became even more unclear than the ones above!