You really should look to get the external IP' s on the LAN side of the router. (this would be a ' routed' solution. What you currently have is a NAT solution.
You DO NOT have to use WAN2, as you have a class c mask, the IP' s you are talking about using on WAN2 anyway is in the same range as WAN1. So you cannot do that anyway (except in very very rare setups).
So, forgetting WAN2, this leaves you with two options if you cannot get a routed solution. They are;
1) get a route added to the ActionTec router, saying to your internal subnet next hop is your fortinet WAN1 IP. This prevents you having to perform a second NAT on the fortinet.
2) Turn on NAT on the fortinet and put up with the double-NATTING.... (bad practice).
So, after deciding the above, all you need to do is add the second IP (.32) as a VIP on the WAN1 interface (you have have as many IPs on the same interface).
Then you just setup the policies as you want, with what you have said, i would setup an incoming policy for the relevant ports to the relevant IP.
Thats it, job done.
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