Yup. In my camper I have the outside omni directional (with a sideways pattern) antenna mounted on the roof and the inside directional antenna mounted on the ceiling pointed down. Very effective at avoiding the antennas talking to each other.Just noticed this thread. I'm currently working on my own cell booster solution and I reached out to a buddy who designs these systems for a living. He offered lots of great info with regard tuning and and optimizing my signal depending on my provider. One very interesting nugget he offered was how to properly place your in-car repeater. All too often you see these configured with the antenna mounted in the rear of the vehicle and the repeater is mounted in the front of the vehicle with the repeater on or behind the dash (facing rearward). The problem with this configuration is the reflection you create when you point the repeater in the direction of the external antenna. In order to avoid excessive reflection (i.e "echo" in RF terms) you should try to point your repeater in the opposite direction of the antenna.
Just passing along the info.