This paper describes the research and development process of an in-vehicle user experience using Skyline, an automotive prototyping platform created in Intel Labs to empower interaction designers and user experience researches to rapidly and iteratively develop and test in-vehicle user experience concepts. The paper describes the hardware and software components of Skyline in depth and how to configure them to suit individual researcher needs. The paper also presents a case study to exemplify the design making process that Skyline enables. From ideation to use-case creation, prototyping and validation through user assessment, the paper showcases the benefits of capturing early qualitative user feedback as support for rapid prototyping walking through a study titled Agency vs. Control and the associated interactions inside the cockpit. Ten defined use-cases are developed and integrated into a hero scenario in Skyline. High fidelity HMI concepts are tested and validated over the course of six months with feedback from a total of fifty users.