GTA V Guide : Friends Reunited : Planting the Explosives Without Being Seen XBOX 360 PS3 PC
After you get out of the car select the sticky bombs. Walk up behind the closest marked trailer and plant a sticky bomb on it. Then go towards the trailer next to which two guys are on a bike. Plant a sticky bomb on that trailer too and sneak close to the guys on the motorbikes until they leave:
Next go to the left and over the road. Go behind a trailer to get to the next closest marked trailer and plant a sticky bomb on it. Keep walking around the outside of the camp to get to the next marked trailer and plant a sticky bomb on it. Go past the trailer to the left and over the road:
Hug the trailer on the other side and go left as soon as you get past it. Sneak up on the guy talking to the trailer and attack him. Then plant the last sticky bomb.