Speaker on Spectrum Dash-8

[andylvtrains]

I am thinking about installing a QSI sound decoder on a Dash-8, using a high bass oval speaker with enclosure, like the one at

http://www.ulrichmodels.biz/servlet/the-419/1.55%22-x-.72%22-x.32%22/Detail

that would fit under the loco body behind the cab.  I know some recommend a round 1.1 in speaker instead.  Where could you find the room to install the round decoder (without chopping too much of the inside if the loco)?  Any suggestion, lessons learned?

Thanks