hi ok i'm some kind a newbe too but i'm going to explain to you
U have to make trigger wich detect u destroyed the BMP:
Activated"NONE"
type"NONE"
condition"getdammage bmp>=1
onactivation""1"objstatus"DONE";obj1c=1
ok now the enemy reenforcements:
just place them somewhere you want to let them come from,give them a move waypoint at the base where they are now,next give them waypoint SEEK and DESTROY at the place where u want them to look after u destroyed bmp
In the condition field of the waypoint MOVE in the base,you write"obj1c==1"
if all good if u destroy the bmp the reenforcements will come to the location of the seek and destroy waypoint and they start seeking to destroy
hope u can do something with it