I tried this with OpenVPN a while back and it was a spectacular failure because keeping the tunnel open also kept the cellular connection active and that sent battery consumption through the roof. I'm talking about 8-10 hours "standby" time on a modern iPhone.
Is that not a problem with your setup?
I looked into on-demand but is required a mdm profile and that seemed more trouble than it's worth.
I looked into on-demand but is required a mdm profile and that seemed more trouble than it's worth.