I just had my mild steel headers ceramic coated, inside and outside, given that the main objective (apart from the nice aesthetics) is to keep engine bay radiant head from the headers down to a minimum.
The coating process took a week and only cost AUD280.00 (about USD260).
The headers came up a treat... looks like softly polished stainless steel. I can't decide whether to put it on the car or hang it over the fireplace as a piece of modern art
I have to wrap the headers in my 24 Hour of Lemons Milano in the area of the motor mounts. I leave everything else un wrapped.
The heat from the headers damages the rubber in the motor mounts. It looks charred.
On my GTV6 I used Swaintech coatings on the headers. I have not run them yet but I hear good things about them. Swaintech coating is very durable but not as pretty as some of the others. It is more form over function.
I have been wrapping my headers on several of my cars for a long time and I even wrap the single pipe all the way to the muffler to keep heat out of the interior. To avoid any moisture-rust issues on the steel tubes I first wrap the tubes with a layer or two of heavy duty aluminum foil from the kitchen. This blocks moisture from the steel and the aluminum is happy in the high temp environment. In keeping the heat in the exhaust system the gas flow velocity is higher for better scavenging. DC