I too would like to improve my rear speaker situation and am thinking about
building two custom boxes to fit on either side of the rear heater. I'll
give up the storage space if I can get the current"truck box" speaker boxes
off the van floor.

The one fly in the ointment seems to be that black pipe/bar that runs the
width of the seat bench.  I don't have a problem with the seat bench being
supported by the speaker cabinets, but how is that bar removed and what
would be the penalty of cutting it off close to the pivot points so I could
have more space to purt the boxes in.  I currently have a pair of Rockford
Fosgate 8" Punch woofers and that's more than enough bottom end for this
couboy.  Anybody modified that bat and if so, how did it turn out?  Thanks
in advance for your advice.

dimwitted mose and FLying Squirrel