I would think that these splitters are wired in parallel:
http://partsonsale.com/learnwiring.htm
So it would likely be a good answer. It looks like you would need 8 of these small panels
to get near what the power adapter provides (or the USB plugin adapter could provide).
That would make using the splitter with larger panels a real possibility. Two five watt
panels might be a workable compromise with size, cost, and flexibility.
Perhaps two of these:
http://www.northerntool.com/shop/too...4313_200494313
It is looking like you will need a surface area of panels (given the stats for these panels)
of about that of a 24" monitor, to have something that can charge up a device like the
libre, in a reasonable time. As you mention a battery in the circuit is a major improvement
(but an added weight) and your project is sounding like a good "transportable" option.
For this sized project you might consider any unused UPS batteries that you might have
on hand.
Luck;
Ken