First build the bridge, get the tank across and to the point where you blow the doors open at the fuel dump. Next this is where it gets sneaky. I make it inside where that truck is and where that door leads to the roof. Next I hide behind one of the wall waiting for an Axis to go up. As soon as I hear the door open I run behind the Axis guy who just opened the door. I kill him as hes climibing up the ladder then drop down and plant the bomb. 
One time one guy was like “damn good job covert ops”. but there was no covert op, just a single engineer that got the job done. Sometimes as an engineer you gotta be twice as sneaky as a covert op to complete the objective.