Choosing the right AP router for my task

I want to buy a AP router and install OpenWRT on it for us in a RV camper. I envision setting it in Client mode and plugging in the local LAN devices and also connecting mobile devices like laptops to the network.

The goal is to only have to configure the AP router to connect to a Campground WiFi or to a Mobile Hotspot, then all my other devices would work without configuration.

Obviously I'd need some hardware that has the capability to use part of it's wireless hardware to setup the Client connection to the outside world and part of it's wireless hardware to connect to the local devices like laptops.

So what hardware will do this and run OpenWrt??

Nearly every chipset / driver can do that with OpenWrt. There is also a software package called Travelmate which simplifies this use case.

I started searching routers that had OpenWrt installed and found some recommendations for the GL.inet Slate (GL-AR750S-Ext).

Is the OpenWrt they install the same as what is available in the project code. Should you replace the routers firmware with what is on the OpenWrt site for that router?

Or use the GL.inet Slate as is with their factory updates since it's OpenWrt installed??