> anyone tried an Evaporative cooler?

Evaporative coolers will only work in an area of very low humidity.  I found
wet towels to be very effective last June while touring New Mexico in my 85
Westy without a working air conditioner and with the heater valve stuck
open.  :o)  They would dry in no time at all and, in the process, become so
cold it would almost be painful to put them on my arms or neck!  If you're
driving in the hot, muggy Midwest, I doubt that evaporative coolers would be
of much (any) value.

> Now all I need is a solar panel

A 50 or 75 watt solar panel will install very nicely on the fiberglass roof
of a Westy.  Check out my web site for details.

http://members.fortunecity.com/davebaker1/westy/westy.htm

Dave in KC