Rather than in-wall mount a VP150 why not use the W150 as the in wall portion looks to be on y 3.5 inches deep.
http://www.axiomaudio.com/wallspeakerw150_main.htmlIt looks like it has the same specs as the VP and it’s designed to be wall mounted. I think it will certainly look better sticking out of the wall than the VP150. Since the VP150 is already enclosed (no ports) I don’t think you would really be loosing anything by switching to the W150 which might actually sound better sticking out of the wall than the VP150 since that’s how it‘s designed to be mounted. Also looks like they‘re the same price.