Device on Specific WAN

How do I set a single device to always use a specific WAN?

Searched and clearly not using correct keywords.

Is this the correct setup?

Well, you have it “almost correct.” The algorithm, you want is “enforced.” If you change your example from “persistence” to “enforced” that’ll probably get you where you want to go. In the example which follows we used IP address as the source. You used MAC – either is fine. (Check the Peplink documentation – there is a nice discussion there which described the meaning of the various algorithms which may be employed.)