I have just test this, handle damage eventhandler works out of the box. I do not knew why its not working for you i think there is something else going on.
Destroying the Caches with Satchels or Charges has always been the bane of my existence with this script. I tried a lot of different things however it did work at one time. It could simply be the changed the way the event handler get handled in the latest versions. In the end, I wanted the cache to be able to be destroyed by most explosive types including aircraft bombs. Never got around to really working that out.
Why then you limited it to only pipe bombs, checking given damage (>= 1) would be enough.