I didn't notice that you're using a 500A fuse. I was surprised to see from your picture that Littelfuse makes Mega/AMG fuses bigger than 300A. I ended up using ANL fuses instead, because they were available all the way up to 750A. Anyway, I found this Mega/AMG holder rated for 500A, and it's made by Bussmann, so it should be good quality:I appreciate your time and suggestions, however this holder is rated for a max of 300A.
https://www.amazon.com/dp/B001PYSUP2/?tag=wranglerorg-20
Incidentally, I found conflicting ratings on that holder, but this is direct from the Bussmann catalog, showing 500A capacity:
