Type I post-main-sequence nebulae appear to be characterised by a range of unusual, and in certain cases extreme physical characteristics, including high velocity (and possibly high mass) outflows, and anomalous He, N, and C abundances; a feature which is almost certainly indicative of high mass nebular progenitors. The authors have acquired high resolution VLA mapping of five type I nebulae, with the aim of investigating the inner core structures of these sources.