Remote hosting Unifi Controllers
Make sure there is a VPN setup between the controller host site and the wifi remote sites
Controller can be hosted on TrueNas or easy mode install via CloudRon.io
if hosting on docker the inform IP is the docker host not the 172.x.x.x address of the guest
also backup often and document the SSH keys for each site. then if something goes wrong you can remotely login to each AP and reset it.
Video with settings walk-thru here
Unifi document with inform options here