What kind of run time do you get from your 20" bar? Mine draws 7 amps and I am worried it will drain the battery pretty quick.
Here is a very technical explanation of rated battery capacity.
Might help you choose a battery size.
http://www.allaboutcircuits.com/vol_1/chpt_11/3.html
How did you like the cube faceing out the sides? did it work well for you?Was able to sneak outside for an hour and Installed two of the four work lights. Feel rigid mounted to the roof. Hooked em up to a temp power supply to see how they looked. I'm happy. I'll run the wiring and install the switches when I'm done mounting.