I don't think it has enough ventilation. I would imagine there is no more than an inch between the bottom of the top tub to the food/hardware cloth of the one underneath it. Also, melting ventilation holes may add air flow, but it gives them a chew-point to plan their escape.

All in all, decent idea, but I think sticking with "traditional" racks is better.

It is too late now, but I think if you replaced maybe a ~3" strip of the tub across at least 2 opposing sides for ventilation, it would provide as much, if not better air flow compared to the holes, and it would not encourage chewing.