It all depends on the installation investment you want to make. The RV video posted above doesn't really need to be concerned about prop distortion as it doesn't need to look in that direction, however mounting a gimbal may require a significant LAME investment. If you simply want to put a camera in the cockpit and have it film out the front to see where you are going, you'll need the filter. If you only want footage facing forwards and no control over where it points, the GoPro session 5 would be fine (wing mounted), but batteries aren't interchangeable so a Hero 5 would offer more flexibility.
Mounting a consumer grade SLR style stabilisation gimbal inside the aircraft (anything up to $1k) with a Canon D5 could work well. The video I posted above is filmed on a D5 for the studio scenes and skateboard unless noted otherwise as GoPro.
The biggest problem I find with GoPros and gimbals is managing the batteries and chargers. So many USB ports are required, it all gets too hard sometimes.