I think what some people have done is just pad in the area where the rear sub goes in the gt model and use the whole enclosure without fabbing a box?
I don't see why you'd get the rear speakers done personally, just a 2 channel amp and the 2 front speakers and leave it without a sub until you can do that. But then again, imho decent speakers don't need a sub separate.
I'm tempted by the hertz mlk165's but they're too deep for the doors I think
I have hertz hsk 165's front and back
Are the mlk's that much deeper?