One thing is the spec code that is used on the material file and other is the managed materials that are used on the .truck file people. By putting the spec code on the material file, it makes a 2 faced body automaticly using the same texture, when using managed materials it DOES NOT.
And what Donelly says is correct, since Johan's tutorial is dedicated for users that use the "Managed Materials" (from what i can see) for their trucks,im not very sure and would not like to start a discussion about it, the spec code for that is used on material and causes it to have an inside face with the same paint as i already mentioned, was given by Chris Hamilton when he relased his updates (I think), few of his trucks had it, also i used it for some of my trucks, for example, Zombie.
What's the diference between both? I don't really know, but they look pretty similar, but being honest the managed materials give a better look to the truck IN MY OPINION, also i think if DanDon wants to make a tutorial on how to use the material spec code and have a fiverglass face without glichting it's a good idea, but i recomend, IN MY OPINION, that people use managed materials since their way easier and better for a trucks body, i also request that someone please make a tutorial on how make spec maps for the managed materials beacause it would be very usefull for a lot of people.
This is just what i know..... DO NOT START A DISCUSSION PLEASE, IT'S NOT REALLY WORTH