Hmmm. I must tread lightly here. Based upon the angular shape of the vehicle I would assume that is was actually made up of separate plates that were welded together.
The way you have created the hole will work but the topology is a bit messy and the hole may not need to be extruded inward at all.
Because you have constructed the chasis as a single object to cut the hole and not have triangles and ngons you will need to carry the geometry around the entire model. You may be able to reduce some of the edges by merging 3-1 though. Ngon's on planar surfaces that will not be deformed will render just fine but in a studio pipeline they might raise eyebrows as will triangles.
Another approach might be to construct the hull more like the way it was actually constructed as a collection of plates. This would make adding the hole a bit easier as you would not have to route geometry around the entire model by localizing it to the front plate.
You could also do away with the need to smooth and could go with just edge beveling. This will reduce texture stretching as well.
"If I have seen further it is by standing on the shoulders of giants." Sir Isaac Newton, 1675
Last edited by ctbram; 01-04-2012 at 07:54 PM.