Do you have a decent min/max tester that you could leave hooked up for a couple of days?
I would consider it possible that the bulb problem is a perceived problem. I have had customers insist there are wiring problems because the bulbs they bought were blowing prematurely, and nothing was wrong, either bad batch or they were stored in a place subject to vibration. Recommend long life or 130 volt bulbs. IT is possible it is a different problem form the smokes.
I have had problems with firex in the past, but the recent ones seem to not do this as much. Look for water condensation in the box. I have had water drop down from conduits and drip on the back of the unit and cause this problem. If it isn't conduit, maybe an opening in the box.
