As I said previously, the tail light assemblies are reproduction. Considering Al's comment, I shortened the mounting brackets for the bulb sockets to make sure the bulbs couldn't hit the inside of the tail light buckets. I then replaced the bulbs for the fifth time in about 4 months. Since then I have driven the car about 15 miles, and neither bulb has blown. Looks like the problem is solved.
Thanks guys for all of your thoughts.