There is that rule of backups, like 2 copies and 3 locations or some variation. If you only have one NAS at home, you better make it double, essentially one is a mirror or backup of the first one. Then, ideally, you have something offsite, or at least some distance away.
I also have an HP DL 380 G7 I got a few years ago. The only issue I have is it does not like non-HP drives and makes the fans go 100%, so I had to hack the fans to make them quiet or something.
As for the seed on paper, this is my procedure now.
1. print or write seed on paper.
2. paint both sides of paper with diluted elmer's glue to seal it.
3. after that's dry, put it in epoxy resin.
Now that's water proof, but not fireproof. So you can get either fireproof container or safe or envelope, or make sure it is surrounded by at least 1 to 2 inches of concrete on all sides (think of John Wick burying his gold coins in his basement, that will survive a house fire.)