The Campervan's router is private and I suppose if I disconnect the card's data it will connect to the WiFi.
The UNI is "allways" connect to the WIFI
And if your router have a working SIM your campervan WIFI can connect to the internet.
To config the UNI you need to access 192.168.33.1 and change the UNI IP adress to the one your WIFI in the campervan use.