The OP asked about heat reduction. The nature of the construction of headers results in much greater surface area and less mass. That's hard to overcome with a coating. Further, a polymer bound coating will be thin and so have little insulating value. The pipe outside temperature is unlikely to be measurable reduced. However, because the polymers (and most fillers) have poor conduction compared to the steel, there will be a reduction in transfer to the air. The ceramic coating with no binder is thicker so should provide more insulation. Whether it reduces transfer to the air better or worse than the polymer coatings would need to be tested.

The third means of heat transfer is the radiated heat. Generally, lighter, brighter surfaces are the poorest in radiating and absorbing radiated heat. Chromed pipes and highly reflective gold, silver and white surfaces would be the best in reducing the radiated heat. So lining the firewall and doghouse of the van with these materials would reduce the radiated heat to the interior. That won't help the conducted and convected heat transfer. Blankets and other insulations are the best for that. But wrapping the pipes can shorten their life, so its a tradeoff.