The alloy thermostat housing on a manifold I'm working on has corroded in places, I've cleaned all the white powder away and lightly waxoyled it, but is there anything I can do to prevent further deterioration?

Can you have it shot blasted and then annodiesed?

normally the corrosion is on the pipe stub where the hose has been weeping hot coolant onto it? Light bit if sealant when you fit the hose

Make sure you use the correct type of anti-freeze coolant at a high enough concentration.

On a fully cleaned out system I would use an OAT long life coolant at 50% concentration.