Trigger activated by wounding units

[Tom_Pynchon 10]

Is it possible for a trigger to be activated when – say – half the members of a team are wounded and incapacitated?

I’m working on a mission where a special forces team must advance across a small meadow to clear a compound after an airstrike. Right now, I’m using a trigger with the (!alive unitname) OR (!alive untiname) ... script to move a gun truck up to provide suppressing fire when any member of the team is killed.

What I’d like to happen instead, if at all possible, is for that gun truck to come up and lay fire on the enemy when, for instance, half the team is damaged and cannot advance.

Thanks.