Rolls-Royce Control Systems supplies engine control and monitoring systems for aviation applications, and is required to design, certify, and deliver these to the highest level of safety assurance. To allow Rolls-Royce to develop safe and robust systems, which continue to increase in complexity, model-based techniques are now a critical part of the software development process. In this paper, we discuss the experiences, challenges and lessons learnt when developing a bespoke domain-specific modelling workbench based on open-source modelling technologies including the Eclipse Modelling Framework (EMF), Xtext, Sirius and Epsilon. This modelling workbench will be used to architect and integrate the software for all future Rolls-Royce engine control and monitoring systems.