Review on 📶 NETGEAR Nighthawk 4-Stream AX4 WiFi 6 Router with 4G LTE Built-in Modem (LAX20) - Ultra-Fast AX1800 WiFi (Up to 1.8Gbps), Expansive Coverage for 1,500 sq. ft. and Reliable Connection to 20 Devices by Rob Dixon

This router is the perfect solution for me. It's hardwired to my Airstream, and since it has a (roughly) 12V input, it's powered only by my Li-Ion battery. No AC power adapter and associated DC-to-AC power loss. WAN input on the LAX20 Nighthawk. LAX20 prioritizes the WAN signal and switches to cellular networks when there is no WAN connection. The ideal solution. The failover process takes about 60 seconds, so unfortunately there is some downtime during the failover. However, it is still automatic! Another note: I originally bought the LAX20 for Google Fi compatibility (uses all three from Sprint, T-Mobile, and AT&T). Since then I've given up Google Fi in favor of a cheaper and better US mobile alternative. I took a chance and went with US Mobile's Verizon plan, which offers "Unlimited to Everything" with no data cap. LAX20 works with the Verizon network! I've read reviews here that said otherwise, but I've seen firsthand that this actually works on Verizon. Remember to update the LAX20 APN field to VZWINTERNET. All in all, this is a fast router that suits my needs very well.