My final build will be with a WP-40, since the price can't be beat -- but the wavebox design will allow for an mp40 worst case
Also it might be note worthy that there was much leakage around the MP40 outlet (what can you ask from a 2-minute, make-shift, hack job)... so with a tighter build things should be very slick - and with glass it should be more stable than 1/32" plastic
BUT, it showed the design will work, and might be a wavebox revolution