Most solar panels have diodes that prevent the current from back-flowing from the battery to the panels. And decent charge controllers will prevent this also.
The instructions with my 3 charge controllers also require to be connected to the battery BEFORE connecting the solar panels. The onboard microcontrollers need battery power to perform their function.
No need to ever disconnect panels at night.
Pointing them South will net good results. A tracking system would do even better, but they aren't usually practical.
Having the panels in the sun, but not connected, is not a problem. No current is flowing.
I clean the solar panels on my roof with an RV brush, and the same soap I use to clean my vehicles and camper.
Very few charge controllers are weather resistant. I had one that was, and it eventually failed. All the ones I have out of the weather are doing fine, despite living in a 90+ degree garage for years.
Here's an online wire calculator. It's the one I use:
http://www.freesunpower.com/wire_calc.phpYour 120W panel can supply 10Amps. At 30', 8 gauge is the recommended size wire for a 3% line loss. I use welding cable, which is very flexible. It can be easily coiled, and will lay flat when uncoiled. I buy mine from this supplier:
http://www.wesbellwireandcable.com/Welding/Welding6.htmlGood luck with your project!
