It wasn't obvious to me that you can create a custom qml object just using qml in a text file. Create a qml file to define your object in the same directory as the code that calls it. The file name sets the qml object's name.
It's very similar in effect to inheritance in C++.

I think your creation code should be more like this:

@ // dynamic object creation
component = Qt.createComponent( qmlFileName );
if ( component.status == 3 ) // enumeration 'Component.Error' == 3
{
// Error Handling
console.log("Error loading component:", component.errorString());
}
else
if ( component.status == 1 ) // enumeration 'Component.Ready' == 1
finishCreation();
else
component.statusChanged.connect( finishCreation );@

here's the function it references:

@function finishCreation()
{
if ( component.status == 1 ) // enumeration 'Component.Ready' == 1
{
var disp = component.createObject( _rootItem, { "parent": _rootItem } );
if (disp == null)
{
// Error Handling
console.log( "Error loading plugin into display area" );
}
}
else
if ( component.status == 3 ) // enumeration 'Component.Error' == 3
{
// Error Handling
console.log("Error loading component:", component.errorString() );
}
}
@

Note that this code sets the VISUAL parent of the created item. If you don't then inheriting parent properties doesn't work