Kurt is correct about the Schottky diode.
I figure the panels working voltage at about 14V, without a diode. The diode voltage drop will make the panel barely able to charge a battery.
A Schottky diodes voltage drop is only a little bit less, but that little bit can make quite a difference when operating at the edge of works or does not work.
The concern about a higher operating current in one panel damaging another is unfounded.
Each sub-panel will supply what it can. Even if one panel can not make any current at the time, nothing will go backwards through it.
For output, make sure no cell is shaded. Shading one cell will drop the output of that sub-panel to near 0ma. The shaded cells voltage is lost, and it uses voltage from other cells which are trying to force current through the shaded cell.
It will not cause damage, and current from the other 2 will not go backwards through it, but the output of that sub-panel goes to 0ma.
If this panel is for camping, I would be very tempted to not use a diode at all.
Connect the battery in the morning, disconnect the battery in the evening.
G-