gistfile1.hpp

// Main Config
class CfgVehicles
{
   class Car
   {
     // all kinds of settings
   };
   class Stryker: Car
   {
      // all kinds of settings
      class TransportMagazines
      {
            // all kinds of items
      };
   };
};

// some other config
class CfgVehicles
{
    class Car;
    class Stryker: Car
   {
       class TransportMagazines;
   };
   class mySuperStryker: Stryker
   {
      class TransportMagazines: TransportMagazines
      {
          // some stuff
      };
   };
};

// Alternative
class CfgVehicles
{
    class Car;
    class Stryker: Car
   {
       class TransportMagazines;  // You can leave this one out now
   };
   class mySuperStryker: Stryker
   {
      class TransportMagazines
      {
          // some stuff
      };
   };
};

gistfile2.hpp

// Main Config
class CfgVehicles
{
   class Car
   {
     // all kinds of settings
   };
   class Stryker: Car
   {
      // all kinds of settings
      class TransportMagazines
      {
            // all kinds of items
      };
   };
};

// Some other config:
class CfgVehicles
{
    class Car;
    class Stryker: Car
   {
       class TransportMagazines
       {
             // Add stuff
       };
   };
};