The new case is 10mm thicker at the top and has internal fins.
The 3000D really needs it least of all as it already has a bunch of aluminum in the case.
We changed it up primarily for a new model we haven't released yet, the SAX-250.2, which I found to run a bit too hot when bridged with the older style casing when I tested the prototype.
The Class-D amps already ran quite cool in the "old" casing.