I don't have a full answer for you but our Milestone came with the Winegard antenna but it wasn't fully ready for use. There are two Winegard lines, one is the main antenna originally designed to pull in TV signals better, and then there's an advanced Air+Gateway option where the antenna has an additional component inside, and there's a router module that you install inside the coach. Our Milestone came with the basic antenna and no gateway, but the wiring was installed and we have a junction box in the ceiling of the master bed with a label on it advertising this. You may want to look for that and also open your actual antenna cover (it's just a weather cover) to see what's inside to know what components you are missing/need to add.
If you have all the needed components my UNDERSTANDING (I've never done it) is that what you really want from Verizon is a data SIM card on your plan, because you can just put that into the Winegard and be up and running. If you want to use an external Verizon router I don't know. Some services like Starlink have Ethernet ports (albeit often as purchased add-ons) that let you use an external router or even replace the base router if you know how. Studying a pic of the Winegard Gateway (
https://www.amazon.com/Winegard-GW-1000-Gateway-WiFi-Router/dp/B07XLTRJ72) I don't see any ports like that so it may not be possible. You may be blazing new ground here...