I tried to monitor the sun and how it hit roof area near where the IMS is, but it looks like the car is actually in the sun for a good amount of time before the alarm triggers (when it triggers, since it doesn't trigger every morning).

I'm wondering if maybe some connection to the IMS is loose and when it gets cold enough, metal contracts so the connection becomes an open. Then when the temperature warms up (i.e. via the sun), the metal will expand and make a connection again and that trips the IMS.