The Spitfire unlike the car it is based on the Herald has sills which are structural and are an important structural component on the Spitfire. The Herald has extra outriggers on the Chassis which is missing from the Spitfire chassis, I know these extra outriggers would add weight but in my opinion they would have been better kept for the Spitfire Chassis as this would have made the Spitfire even stronger (especially being the fact that being a convertible there is no roof to add strength). On some cars you can tell the sills are shot by the fact that the doors do not fit properly and the car is starting to fold in the middle. On my car the only reason why one door would not fit was the fact that the door hinges we slack so was not expecting the sills to be too bad as they also looked ok, how wrong can you be.
The first job is to remove the outer sill, this was not a difficult as I thought as once I got through the layers of paint and filler it was well rusty so came of easily with a plasma disk in the old angle grinder. As you can see in the photos below once the inner sill was removed it was not a pretty site.
With the floor replaced the first job after cleaning up any rusty and damaged areas is to fit the inner sill. When I changed the floor the old inner sill was still in place as a reference for the location of the floor, I could then use the floor to build out to the outer sills. To check for fit and alignment the door was put back on and adjusted to make sure it closed correctly and the gaps were right. The photo on the right below shows the inner sill being trial fitted into place, you can see the jack under the floor to give support and the red bar across the photo is an adjustable door brace to give extra to strength to the door gap. One I was happy with the trial fitting the paint was removed from the welding surfaces and primed with weld through primer before being tacked into place.
The lower A post is a place where Spitfires love to rust and mine was no exception, it had been repaired in the past and because of this it was not repairable again as not only had the repair rusted but the original panel had been mess about with so fortunately a new panel is available. This new panel is brilliant, it would be very difficult to try to make one yourself ad a pressing is the only real option. It is important that the bulkhead and front section is either supported well or plenty of measurements must be taken because when the A post lower is remove the bulk head becomes very floppy. As I said above the repair panel is great but it still required a lot trial fitting and readjustment until it fit well. Once it was welded in it made the foot well area look factory fresh although once the carpets are installed it will not be seen.
With the A post lower repair fitted the sill middle could be fitted. Before this was fitted I sprayed a couple of coats of weld through primer on the inside of the inner sill to give a bit more rust protection. The middle sill closes off the inner sill and makes it into a box section to give extra strength and when the outer sill is fitted again this will make another box section on the outside.