We had something like the unit below on our caravan but it was a 2G unit ( 2G since shut down.) This 2G tracker had a GPS Aerial as well as a socket for an external aerial and I connected it to a Mobil phone Broomstick aerial. The unit below only has the GPS aerial and to me an internal aerial for SMS's etc. but would be sufficient for areas where you have mobile phone coverage on your smart phone... and of course only use the Telstra network, and suggest with a Geo Fence setting..

www.ebay.com.au/itm/3G-GPS-Tracker-Anti-Car-Theft-GSM-Hardwired-Kit-Yacht-Boat-Caravan-Live-Tracking/172737116514

You may need to specify the Telstra network when you order, we did this when we ordered our Dog Tracker (only used when away from home)

To check the location of our van we would send the tracker an SMS with Pin Code and it would send back the GPS Co ordinates that went into a Google Maps app on a Smart phone/Tablet with Sim and showed us the street/bush location.

With the Geo Fence setting, if the van is moved out of the set position by a 100m or so you are sent an SMS alert.

Note that was our 2G unit you would need to check the functions of the above unit.

Peter