Nando,
Thank-you, Mouser.com was what I was looking for - a place that carries everything electronic.
I was puzzled at the diode ratings you suggested, 30 volts at 10 amps. A string of 5 in series would be 18 volts X 5 = 90 volts at 3.5 amp. I've studied the diagram on the back of the panel, done some back of an envelope sketching, scratched my head, and I think I've got it.
A "blocking" diode would be in series with the entire string. I would need only 1 per string and would need to be sized to carry the load of the entire string, in my case 90 volts @ 3.5 amp. It's purpose is to pull the entire string out of the circuit if the power is trying to flow backwards, such as night discharge.
A "bypass" diode (I'm still a little fuzzy on this one) is in parallel with each individual panel. 1 per panel sized to carry the load of 1 panel only, in my case 18 volts at 3.5 amp. It provides a circuit around an individual panel that is trying to absorb instead of provide current.
These particular panels are constructed as 2 X 6 volt circuits, therefore 2 diodes per panel, carying 9 volts at 3.5 amp.
From there, always over size a diode by at least 2 X the expected current, therefore your suggested 30 volt, 10 Amp suggestion.
Am I close?
-Henry