Is the unit moving?
If not, assume its on defense and avoid sight. Set up the sniper on the second-highest level of the building and the rest camp out near the stairs up from the first floor of the building. Put the gunner near the window facing out of the second floor.
If its moving, quickly (and stealthily) move to a building 4 buildings in front of them and prep for an ambush. Set up the sniper and a rifleman behind the units, however, for example the building where the unit is right now (assuming they moved a few buildings farther).
Optionally, if they know exactly where you are get the forget out of there.