With the development of electric motor vehicles and autonomous driving systems, the domain of automotive sound design addresses new issues, and is now concerned by creating suitable and pleasant soundscapes inside the vehicle to ensure comfort and safety for the users. In particular, the integration of informative, alerting and intuitive auditory feedback becomes essential. For instance, previous studies proposed relevant sonification strategies to convey the information about the vehicle dynamics in electric cars. However, while the sound feedback is informative per se, users reported its lack of blending with the surrounding natural sound field of the vehicle and the artificial character of the sound itself. The challenge is therefore to integrate such sound feedbacks in the car interior soundscape in natural way by adjusting both timbre and spatial parameters. In this research, we propose an experimental setup to investigate perceptual integration of synthesized and environmental sound streams spatialized in car cockpit. By combining synchronized 3D acoustic field measurements and 3D video recordings at seat viewpoint, we constructed immersive audiovisual environments in the laboratory to get close to ecologically valid driving situations while avoiding time consuming in-situ experiments. The proposed setup also allowed to virtually control sound sources (both their timbre and location) in the car interior and to study the spatial perception of the overall designed soundscape before vehicle integration. While we here address the case of car cockpit, this approach may be used for different contexts in which sounds need to be spatially integrated in natural soundscapes