I recently bought a job lot of cast iron cookware at an auction to get the camp oven (Metters 14") that was part of the lot. Included was three cast iron kettles and two oval boilers all in good nick on the outside but heavily rusted on the inside. I've cleaned them up and painted the outside with oven black but want to stop them rusting out from the inside without making them useless to ever boil water in again, any ideas ? poddy dodger.

G'day Mikel,
The three kettles and two boilers I cleaned up using electrolysis and a wire brush, I have just given them a couple of coats of "White Knight" oven black heat proof paint using a brush, I was'nt aware of a paste. On the outside they are all in very good condition and I think they might have been protected with some sort of paint/paste at one time, the makers name is clearly visible both on the sides and underneath but inside is another story, like you suggest I'll just keep them dry.
The camp oven also came up well, inside is as smooth as, the outside has minor pitting but I'm not worried about that, I have seasoned it with olive oil  as I do all my pots.
pd