Can you NAT your CGW behind a router or firewall?
Yes, you will need to enable NAT-T and open UDP port 4500 on your NAT device.

https://www.interviewquestionspdf.com/2017/01/can-you-nat-your-cgw-behind-router-or.html
Yes, you will need to enable NAT-T and open UDP port 4500 on your NAT device.