I was able to install a sony 10 disc changer under the driver seat and it
fit perfectly without the seat sliding against it while adjusting.  You
might also try to put it vertically in the aux battery area if you don't
already have a battery there.

86 Vanagon GL
89 Jetta GL
93 Honda Civic (wife's car)
Hotch
Philly
Richard Hotchkiss
http://www.hotstrings-inc.com