I do modding. But I have to destroy your old xbox casing as I do not have the proper tools to open the casing. What I did was to custom made the case out of mild steel with proforated openings on all sides for ventilation. But be warned, it's not cheap. I have a factory for manufacturing equipment racks so I have the proper tools. It would cost about RM10,000 for a custom made design, inclusive of drawings in ACAD (to feed into the machine) etc.