I just realized that I have been posting my question in the wrong forum, wondering why I'm not getting an answer. :P.
What I have and currently works
I have a functional route based IPSec VPN tunnel using the instructions at https://docs.opnsense.org/manual/how-tos/ipsec-s2s-route.html.
Site A: LAN=192.168.1.0/24 WAN=1.2.3.4
Site B: LAN=192.168.8.0/24 WAN=4.3.2.1
Phase 2 Local address at Site A: 10.192.168.1
Phase 2 Local address at Site B: 10.192.168.8
Phase 2 Remote address at Site A: 10.192.168.8
Phase 2 Remote address at Site B: 10.192.168.1
Gateways added on each site, and static routes exists for making sure the 192.168.1.0/24 can talk to 192.168.8.0/24 and vice versa.
Good so far.
Context
For the purpose of simplification, there is a website http://showthisip.com that displays my public IP address. That host name resolves to 63.247.147.167.
At Site A, when I visit that website from a client on the 192.168.1.0/24 subnet, I am shown the IP address 1.2.3.4, which is expected. That's the public IP of the WAN interface of OPNsense at Site A.
At Site B, when I visit that website from a client on the 192.168.8.0/24 subnet, I am shown the IP address 4.3.2.1, which is expected. That's the public IP of the WAN interface of OPNsense at Site B
What I want to do
I want, when I visit that website using a client on the 192.168.1.0/24 subnet at Site A, to show the IP address: 4.3.2.1. The public IP of the WAN interface at Site B. In other words, I would like to route traffic leaving Site A for 63.247.147.167 through the VPN tunnel I setup previously so that http://showthisip.com thinks I am at Site B.
I add a firewall rule on the IPsec interfaces (both sites) to allow all traffic in. Then I proceed to add a static route at Site A:
Network Address: 63.247.147.167
Gateway: 10.192.168.8
I open my browser at Site A, type in the website address... and it times out.
I trace route and see:
traceroute -n 63.247.147.167
traceroute to 63.247.147.167 (63.247.147.167), 64 hops max, 40 byte packets
1 192.168.1.1 0.347 ms 0.272 ms 0.158 ms
2 10.192.168.8 151.799 ms 151.946 ms 151.913 ms
3 * * *
4 * * *
5 * * *
Am I missing another firewall rule?