Shiltsy wrote:
Basically want a system with max output per square foot of roof space consumed.  If I can fit a 2x4' panel will 100w serve my purposes well?
Yes.  Without any problem as long as there is sunshine.   In the winter, you will want to knock snow off the panel.   
As a side benefit, the number of days you can stay out without power may even double.
Hum, I wonder if you could put a flexible panel (or lots of little panels) on the top of your cargo carrier?   Might be worth looking into.  Someone on here will know.
Enjoy your solar system,
Steve