I haven't worn my kilt to a stated communication of my Lodge or to an LOI, but I would lean towards leaving the sporran off in an ante-room whilst within a Tiled Lodge. I tried my apron (UGLE pattern MM but compliant with GLMA Constitutions) on in the privacy of my bedroom the last time I was in kilt day-wear and found I could wear the apron over my tweed argyle jacket, however, it felt odd. No way I could do so with my PC.