How should I implement 2nd backup for my config

Here is my setup:

• I have two proxmox installations (totally not related) on totally different locations
• on both instances I have a few CTs and VMs
• on both instances I run “backup job” where I create backup to a external USB drive - this is a “first” backup from where I can quickly restore if needed

What I want:

• I want to have a separate (off-site) backup
• I have Raspberry PI with 5TB USB storage
• I want to use this raspi for both Proxmoxs

What would be the best solution for this?

What I was thinking (I don’t think this is the most elegant solution):

• install tailscale on raspi
  • (same on both proxmoxs)
  • create CT and install tailscale on it
  • in some interval push backup file form proxmox to CT and then this CT pushes backup over tailscale to raspi

edit: spelling