Rust under bonnet? PH2

[Malky]

Is this a common problem, for the underside of the bonnet to be quite rusty around the edges? Nothing evident on the top side, just the bottom

 

[Tigger]

I got that on mine, in the edges of the inner-skin I think it is?

A light sanding and a touch of Hammerite Smooth tidied mine up nicely last week