Look at your mesh resolution in the inlet, it's awful:
You've got half a cell covering the entire length of the open area.
I recommend you start with a 2D analysis. It will allow you to greatly increase the mesh resolution that you need for these relatively small inlets. It's not a very realistic model, but it should give you some idea of how you need to structure the enclosure to get the best flow around your hot components.
I would also recommend modeling your mounting fixture. Right now your hot box is just floating in the middle of this enclosure, not very realistic.
Thanks for the reply Amit. I'm not sure how to do a 2D analysis, but I did find how to refine my local meshes for my inlet and outlet lids and am running another sim now. I was also wondering about my wall conditions. I'm just using wall temperature because I'm not sure how to input the correct heat transfer coefficient (the tutorials always have a number to put in there, but don't tell you where it comes from) - do I need to calc that?
I was trying for super-simple, but as you suggested I did add the mounting bracket for my node ("hot box").
I'll upload again after running with the refined mesh.