Lubuntu 20.04 Sharing AirVPN as a hotspot

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So as my QNAP has a habit of being garbage and having constant security issues, I'm trying to entirely isolate it on the other side of the VPN.  To do this I got an old laptop, connected it via it's wired connection to my standard network, threw lubuntu 20.04 on it (very low power consumption, etc) and setup AirVPN on it.  I share it by making a WiFi HotSpot which I then get my NAS to connect to and all is well.  Problem is, I've already had the VPN drop and it temporarily has access to the direct internet again until the connection is restablished.

Obviously network lock would be the ideal situation but I can't get it to work, even when I put the IP range for the WiFi into the routing list as inside or outside the tunnel.  What am I doing wrong here?  It works fine if I disable network lock, but I don't really want to risk it being directly on the open net.