One strategy for Angry Birds Bad Piggies level 20-2 is to “shoot the moon”, flinging the White bird high in the air, just left of the floating platform. Bomb the base of the right tower, detonating the TNT within. All that remains is to topple the left tower with a single Red bird. The score in the video below is 79,620 with a lot of debris left over.
Note, this was previously Angry Birds Bad Piggies Level 19-2. Rovio shifted some chapters around in the v3.0.0 update. More info on the v3.0.0 update can be found here.