Help with new Door_Elevator / PathedInterior

Ok, I've finally tried the new "PathedInterior" class in the HEAD to get sliding doors and the like into our game... AFAIK those are taken from MarbleBlast and should work similar... now the only docu I found was a thread post over here...
Now, as I was playing with it, I realized that there dont seem to be any script changes yet to add PathedInteriors in the mission editor... so I went the usual way and added

%Mission_Item[6] = "PathedInterior";

to common/editor/EditorGui.cs
and

function ObjectBuilderGui::buildPathedInterior(%this)
{
	%this.className = "PathedInterior";
	%this.addField("dataBlock", "TypeDataBlock", "PathedInterior Data", "PathedInteriorData");
	%this.addField("interiorResource", "TypeString", "interiorResource",  "");
	%this.addField("interiorIndex", "TypeS32", "interiorIndex",  "0");
	%this.addField("basePosition", "TypeMatrixPosition", "basePosition", "0 0 0");
	%this.addField("baseRotation", "TypeMatrixRotation", "baseRotation", "1 0 0 0");
	%this.addField("baseScale", "TypePoint3", "baseScale", "1 1 1");
	%this.process();
}

to common/editor/objectBuilderGui.gui...
and of course I have some dummy datablock:

datablock PathedInteriorData(PathedDefault)
{
   StartSound = FootLightSoftSound;
   StartSound = FootLightSoftSound;
   StartSound = FootLightSoftSound;
};

But it doesn't quite work... I get the gui to add the object:
tork.zenkel.com/uploads/pics/door2.jpg,
but I'm not sure what "interiorResource" is expecting (it seems to need the complete filename of my interior, is that correct? Or just the name?)
But where I am totally lost is the "interiorIndex" parameter... what is that? how should I know the interior subobject id? (trying -1 or 0 or 1 etc. gives my an assertion...)

And also, can I add a Door_Elevator object to any other map file? Or do I have to make doors as separate .maps?

Could somebody plz post a little howto? Or add the necessary script changes to the HEAD? Or both? ;)
Or point me to some (MB) documentation maybe?
Thx!