How are you accessing your LAN server now?
I too have the web servers on the LAN and I simply set up DNS on ZS so when if punch in ‘www.mydomain.com’ from the LAN it resolves to 10.10.10.2, same as if I did it fro the WAN and NAT resolved to the same ID.
Sounds like you do not need NAT, and that is not really a task for NAT at all. It would be if you wanted to access port 80 and be redirected to port 8088 for example…
HTH!