Great video, I’m using the same Apache case for my FT-891. I centered the rig in the middle to give even airflow left to right. I mounted the mobile bracket and the body is secured with that, it also helped to center the weight for easier carrying and also allowed enough room to drill and attach the bulkhead connector for the mic just below the left latch.
I was worried about heat as well. I'm using an 857D with Armoloq frame inside of a bag and the airflow is extremely limited. It hasn't quit on me yet. I do try to keep the power down to 20w or below but I've been to 100 watts SSB for an entire activation without an issue. I'm in FL and that was sometime in the summer 😂