If your cargo is only tall at times but not long, you could also do something more along the lines of a Subaru Baja - cut the roof out only over the back cargo area, leaving both rows of seats. With the C-pillar in place, there won't be as much torsional weakening over the rear axle. Then split the existing tailgate - top half goes just behind the second row, the bottom half will serve as a tailgate.

Or just get a trailer hitch (preferably the old OEM ones with a 2" receiver, as that offers greater options) and hook up a little utility trailer. These can tow up to 3500 lbs.

-- Kane ... who has thought about cutting an old 245 to serve as a utility trailer, ala the folks who double up a pickup's cargo by towing another bed from a wreck behind it.
--
Blossom II - '91 745Ti/M46 ... Bubbles - '74 144GL/BW35 ... Buttercup - '86 245GL/AW70 ... The Wayback Machine - '64 P220/M40