After stripping down the underside and having gone looking for any areas that had any sign of the early stages of rust. Now the best thing to do was apply Hydrate 80 rust killer to prevent the surface rust becoming more than that in years to come.
No point being shy with it.
Not sure there was actually any rust up there but can’t be too careful!
Next, masking EVERYTHING before spraying the Dinitrol Protect Super 447.