I would stay away from the plastic ones they aren't rated for electrical wiring. plastic and the heats that get generated from arcing or even just from a poor connection doesn't seem like it would work out well in the end. they serve a purpose but i fear it's not here.
Almost all the boxes in the walls of most residences are plastic. The box is only meant to contain a small arc, the circuit breaker will trip upon an arc, ending the arc. The box is not meant to contain constant shorting. There are all kinds of plastic j-boxes rated for electrical wiring, do your research.
