I had the header on my old FJ-55 header (F engine) wrapped and had no problems with it for many years that I drove it. To help seal up the wrap, I saturated it with silver hi-temp exhaust paint and that seemed to help keep the moisture out of the wrap.

The LC header I have in the 4Runner has the ceramic coating and that seems to help quite a bit. You could always send the header out to Jet Hot and have it ceramic coated.