I have a SOHO and Panorama 5 in 1 rooftop antenna on my RV I primarily use for the MIMO Cell antennas with my Jetpack, but it does have MIMO Wifi elements as well.
I have tried various configs, normal inside all three antennas, 1 roof top, 2 inside, 2 rooftop 1 inside, 2 only inside or outside with one empty port, it all works.
I haven’t noticed much difference either way as my RV is fiberglass its mostly transparent to WiFi. You definitely want all three antennas connected for 3x MIMO other than that the more elements outside seem to help with WiFI WAN and campgrounds while sacrificing speed on the LAN inside but its a very slight difference. If your RV has a metal skin this would be much more pronounced (Airstream).
Right now I think I am running 2 inside one external, but in the end it just did’nt make much of a difference that I could measure. The SOHO does an amazing job at picking up WiFi regardless of antenna location and if I turn up transmit power all the way it will overwhelm the wifi in my house from across the yard through a block wall, my device will prefer the RV, I have to remember to turn it down when home and parked.