Low-energy electron transfer between a Rydberg atom and a target molecule can result in formation of long-lived metastable negative ions. Here we describe a novel permanent-magnet Penning trap designed to examine the lifetime of such long lived metastable negative ions. With the help of ion trajectory calculations, the characteristics of the trap have been investigated and the most effective methods for ion injection have been established. Collisions with SF6, which has a high electron attachment rate, result in the formation of SF-*6 ions which are known to have a long intermediate lifetime. Comparisons between experimental SF-*6 trapping data and ion trajectory calculations are discussed that demonstrate the capabilities of the trap. Future experimental studies are also proposed.