X'pony,
Interesting, I also like to space the batteries. It allows for air circulation, but I also like to be able to see the sides/ends in case there is any signs of deflection or leak.
Our bank is two parallel, series strings; 48V (840 AH), 6V batteries. The other thing that I find works well, depending on the terminal style, is to alternate the orientation of every other battery in each series string. It just keeps the interconnecting cables shorter, and more direct.
The reason that I rotate batteries, is that while we have a 48V bank, we still have a lot of 12V loads (lights mostly, some electronics, a just-won't-die Danfoss/fridge, and one remaining 12V generation source). We use a 12V "tap", paralleled across the two strings, and equalize with a Solar Converter's "Autotransformer" (buck/ boost converter really).
There are a number of handheld refractometers out there. We make maple syrup here in VT, and more and more we're seeing them used for accurate density of sap and syrup. They also make them for testing antifreeze and battery electrolyte, etc. There not cheap, but they are helping you with preventive maintenance of an important and expensive component of the system. (That's how I justified it anyway ;>). The one we have is a Sper Scientific #300055.
DoubleDS,
The tubing is low cost and readily available from maple sugaring suppliers - try googling Leader Evaporator, CDL, or Lapierre. If you use the soft-flex (often used for 'drop lines') you can just drill the caps close to the OD of the tubing and press fit; no glue. I just plug the cap vent holes with silicone.
Best, ~ks