In general the Spitfire chasis tends to come off okay. The amount of oil that the engine tends to leak means that the chasis from the engine backwards is usually coated in a thin layer of oil, providing excellent rust protection.
1. The main place to check is the cross member at the very front of the car. This cross member takes the brunt of the weather and spray thrown up by other cars. Though not expensive to have repaired, it is important due to the structural nature of the car.
2. Another place to check is the bonnet hinge mounts, which should have drain holes in the underside. Although if someone has "repaired" these at some point and forgotten to leave the holes there, they will fill with water and rust through.
At the other end of the scale, the bodywork of a Spitfire can become riddled with holes if not cared for properly. Working from the front of the car towards the back of the car, the places to check are,
1. The bonnet suffers in two main places, around the headlamps and the wheel arches.
The headlamps are protected by an aluminium surround, which is bolted into place with three bolts. However should some of these bolts be missing, then the surround vibrates against the bonnet and will wear the paint away. As this part of the bonnet faces forwards, it is guaranteed to get a soaking in the rain. But beware, the rust starts behind the surround, and is therefore not visible. The rust then eats its way under the paint, and then becomes visible as bobbles in the paint.
Due to the design of the bonnet, with the wheel arches built in, there is not much protection against road spray for the underside of the bonnet. Whilst the underside of the wheel arches are usualy well undersealed, spray can end up on top of the wheel arches. Rust starts here, and by the time it is visible on the outside of the bonnet the damage is done. If a bonnet has rusted in this way, it will probably need new wings and outer wheel arches, the inner halves can usually be saved.
2. The front quarter valences, which were originally metal, are prime targets for rust. They get full exposure to the rain and spray from other vehicles, and they get sprayed with rain by the front wheels. Having said this, most of them don't last and have been replaced with fibreglass substitutes.
3. Next is the windscreen surround. On either side of the windscreen there are rain gutters, which were never well attached at the factory. Consequently rain can be forced behind the rain gutter and the windscreen surround, and rust starts to form there. This is usually hidden by the seal for the door window. However if this is left, rain is able to enter behind the gutters, and run down the inside of the car into the sills. The sills then rust out from the inside.
4. The battery compartment is another classic rust blackspot. Battery acid removes the paint from the bottom of the battery compartment, and spray from inside the engine bay then rusts out the bottom of the compartment. Again this rust is hidden by the battery.
5. The sills on a Spitfire are very important structural pieces. This fact is sometimes debated hotly, but the sills not only detirmine the door gaps, but also provide the mounting for the radius arm of the rear suspension. Road salt thrown up by the front wheels, and rain water running down the inside of the body (see rain gutters above), attack the sills from both sides. By the time rust appears on the outside of the car, the inner and diaphram sills are probably already in need of attention.
6. As a convertable car it is inevitable that rain will get inside the car at some point, and in the Spitfire's case the poor seal between the hood and the windscreen does not help. If rain water is left in the footwells, it will rust the footwells. There are drain plugs under the carpets, and if rain collects in the footwells, the carpets can be lifted, the drain plugs removed and the water drained. However if this is not done, the carpets retain the water and footwells rust.
7. As with the footwells, the doors also have drain holes, and will also rust quickly if they are not used or become blocked. The doors are also easily missed as you have to either feel the bottom, or get down on your knees to see the bottom.
8. The rear wheel arches fair much better than the front ones, however spray from the rear wheels coats the lower rear wings and it is here that the panel tends to rust. Repair sections can be bought for this specific area, as a whole new wing is reasonably expensive. Undersealing the wheel arches, and just cleaning the lower wing section is a good way to prolong the life of this part of the bodywork.
9. The bootlid is a regular rust spot, especially along the trailing edge. The design of the boot is quite good in that the boot has a lip, which the lid comes down over, effectively sealing the boot. However the lid design is not as good, and the corners tend to rust.
10. Inside the boot, the rear valence suffers a similar fate the footwells mentioned above. Again there are drain plugs, but if they are not used to drain water from the boot, the valence tends to rust at the edge which is welded to the boot floor. Water can get into the boot via holes in the rear wheel arches and lower wing sections.
So all in all there aren't that many places where the Spitfire doesn't rust. On the bright side, almost all the panels that make up a Spitfire body are still being made. So repairing a rusty car is not an impossible task. If you're handy with a welder, then the panels aren't that expensive, and that keeps the cost of restoring a Spitfire down.