By far the easiest way to take out a single building is with Hotwire or Technician. They carry enough C4 to destroy a building in one run without revealing that you're blowing it up.

Run into the furthest tunnel from the defense of the other base and run to a safe spot in the enemy base. Since the powerplant is in the back, there are very few defensive players back there. At least in this demo, there aren't a lot of defenders. Run INSIDE the enemy powerplant and use the handgun to take anyone out and plant some proxies near the doors. Place two remote and two timed on the module (You might only need three, but I used four to make sure). Detonate a few seconds later to make sure they can't repair the building before the timed goes off.

This is a quick-striking attack. You have to depend on your team putting frontal pressure on the enemy and the tunnels being relatively safe, but if you get in to the power plant, you could single-handedly win the game for your team.