Preserve R7800 flash memory by using overlay on USB?

My goal is to preserve the routers flash as much as possible. I am using an external USB for logs and stats from collectd, nlbwmon, adguardhome, etc. I have set the folders in LUCI to point to the USB mount in /mnt/sda1. Everything appears good, but the folder '/overlay/upper/mnt/sda1' is still filling with some data from what should be on the USB drive. There's a lot of collectd data being written despite having RRDtool setup and pointed to USB.

Does setting the USB as an overlay drive help with preserving the flash? The USB is FAT32. How should I proceed?

-HNYMAN OpenWrt 22.03-SNAPSHOT, r19540-945b13e369