Pingable IP address for full mesh VTI tunnels

Hello,

I'm trying to decide the best way to establish an address/subnet a customer can ping to ensure our virtual routers are available. This will be over a full mesh BGP set up between 2 of their sites with 2 of ours. I suggested the VTI interface on our side but they require an address beyond the tunnel interface. My current thought is creating a loopback and advertising a /32 on each router.

Thoughts/opinions?