The Sky4 Ranger as installed by Forest River does not have a component inside the trailer. All of the functionality is included in the unit on the roof.
Looking at the wifiranger website it appears there are indoor AND outdoor models do not look like the WiFi Ranger 4 unit as the OP said in his post. " with ranger 4 wifi box on the roof
I think the Sky 4 unit is OLD as it is no longer listed for sale any longer.
I am not sure why gathering a weak outdoor signal, amplifying it then sending another wifi signal thru the roof is a better idea then distributing a clean wifi signal thru a wire into the cabin is not a better idea?
Perhaps FR chose to go 1/2 way and not install the indoor antenna as is shown in the descriptions on the wifiranger website... Fortunately that additional functionality CAN be added for more ROBUST signals from 3rd party or WiFI Ranger.
Both screen shots from Wifiranger website shown below show how they (apparently) recommend the outdoor router be used...
I think adding the indoor wireless would solve the OP problem. My first recomendation ( TPLink) is listed at $25