My in progress repair.......well chuffed with the outcome so far, so thought I'd post a few pics. A lot of rust was removed from the void but the inner sill wasn't holed. Treated with rust killer and filled the void with Waxoyl (which later caught alight when welding!) I decided to plug weld through drilled holes rather than risk trying to seam weld. I joddled the top edge of the new piece and the existing metal down the sides. The new piece is actually more flush than the photos would suggest. Forgot to take a photo of the welds ground down, and managed to get a skim of P38 over the seams....all looking good. Weather permitting I'm now hoping to get it finished off next weekend.
I didn't fill the holes up with weld as was concerned with putting too much heat into the panel. Each hole has been welded though and the panel sounds solid when tapped. Perhaps smaller holes next time?!!!
It puts a step in the metal of your repair panel, so it allows you to overlap your new metal with the existing bodywork for welding them together with an overlap, whilst still allowing the repair to sit flush to the panel. have a look at the pictures again, you can see how the repair piece slides in behind the old bodywork, and is then plug welded through the holes.
I am watching with interest as I have some repair bits coming to fix the small picks in ours. Keep up the great job, one at a time.