Reminder: radials need to attach as close as possible to the antenna base/feed point.
-You can work contacts without radials.
-Any radials you add will improve performance
-Any length is better than none
-Radials close or in contact with the ground will be detuned so precise length/resonance is not critical
-Still radials about 1/4wl long at the lowest frequency would be great
-Personally, I think 8 radials are the level of effort I want to put into setting up a portable operation. You may have different ideas. This number should do a good job of providing a stable impedance and ground plane, in my opinion.http://www.antennasbyn6lf.com/
Rudy N6LF has done some wonderful and easily readable work on vertical ground planes. bill