My cupholder is attached to the heater cover area.   I made it out of
some leftover teak and simply screwed it from behind the cover.   The
sirrius radio in this pic has been replaced with my gauges for Oil Pressure
and Oil temp.   It just so happens that my particular Sirrius fits
perfectly in the ash tray....but I only really listen to that on real Road
Trips of a full day or more...

   There are  stable travel cups, SS and like a Stanley thermos that are
suited to just plopping down almost anywhere in the vehicle that has a
horizontal surface..  My wife always has mine in her Subaru...

  Link to Picasa pic of that cupholder..
https://picasaweb.google.com/112899774170781374478/VanagonMods?authkey=Gv1sRgCJnj78ukqaPufw#5422691687359055010