5N2 Hard drive experience and reco?

I have two 5N2s that I use for backup for medical data. The backup works fine. The first set of drives, WD Red 2T now about 4 + years old and on 24/7, are acting up a bit and while I have had no outright failures, I have had warnings. I don’t mind the slow access speed because of the platter speeds, but I would not mind paying more for a more durable drive set. I realize that the conditions that the drives live in (stacked, small enclosure) is not the greatest for heat control. Any recos out there? Should I be happy with replacing the drives every 4-5 years? Thanks, Ken K