Gl-mt300n 1:1 nat?

I need to set up some 1:1 NAT devices and I’ve got a bunch of GL-MT300N’s on hand. If I can get this to work I’ll probably buy a bunch of AR750’s to use in the final setup (doing the same thing as the MT300N’s) as I’ve got more places I need to do this than I currently have MT300N’s. First off I need to get it working.

I can’t figure out the best way to configure these devices to do 1:1 NAT.

Basically I just need anything that comes in to the WAN IP of the router forwarded to one IP in the network, and any data from that IP that goes out needs to appear to come from the WAN IP of the router. No other mangling required. I’m happy to disable any forwarding or other tools on the router as this is a dedicated task. Even manually editing config files is fine.

Note: There’s only 1 WAN IP on the router. I don’t care about any other traffic, and I don’t really want other devices communicating out the WAN IP.

Can you simply draw a topology diagram?

Basically, as an example:

(Upstream router) <-cable-> (mt300n WAN) <-1:1 NAT in mt300n-> (mt300n LAN) <-cable-> (End device)

Basically I want any packet that comes in to on the router to be forwarded always to, and any packet from should leave the mt300n WAN port as WAN IP range is a /30, LAN IP range is a /24 (but all other IP’s in that range can be ignored).