I keep a Crate bass bus in my vanagon most of the time:

http://www.crateamps.com/html/product.cfm?pid=16

   - Dimensions: 11-3/4"W x 14-1/2"H x 12"D
   - Weight: 20 lbs.

It fits behind the passenger seat really well and makes a decent foot rest
when you spin the front seat around.  The sound isn't too bad and it is loud
enough to hang with moderately loud to quiet drummers.  The tx50dbe would
probably be better for a keyboard.

I have used the bass bus as extra sound reinforcement in a variety of
settings from laptop/portable audio to an electric guitar and bass
simultaneously.  With the included dc 12v input and rca inputs I should be
able to connect to the sub output from the headset but I haven't tried that
yet.

A few of us played in the brief sunshine at eb last year, don't know if the
other members were listers though?

Jonathan Poole
82 ac westy