Hi Steve, I know the MQ is a little Faraday box! I have P-90's with both types of cover. The MQ's will hum when there is a lot of RFI around, but reject it better than the regular P-90.
I just got my Warpig/MQ set, so I'm going to fit that to my Richwood Explorer. I will see how they work together (also see how the Warpig sounds against my Pig-90).
Cheers
Phil