Update to my old problem
I replaced only the circuit breaker near the battery with a ANL fuse and for testing, I ran the heater again. That ANL fuse worked fine BUT the other circuit breaker near the inverter did the same thing, dropped voltage for just a second which is enough to trip the inverter. I replaced the last circuit breaker with a ANL fuse and the system worked fine. Tested it 3 more times after letting it completely cool down between tests. No issues at all. It takes about 12 mins to heater up completely, the inverter fan kicked in twice and turned off as it should, no real heat issues could be felt, and very little battery used so I think it's OK.
Lesson learned on which type of fuse for this application and it had very little voltage drop from the battery to inverter through these fuses. Thank you all for the input and suggestions