Sure. Getting wire to where you want the speakers can be challenging, but you are essentially ' fishing' wire up the wall to the outside points, or pulling outside and running along the outside of the trailer.
If you already have speakers connected to B, you will need to put these in parallel with existing. You will lose some of the volume.
Jim & Kim from Colorado
2014 Eagle 30.5 RLS
2015 Dodge 3500HD SRW 6.7L
Click on my profile for Mods and notes