Fungus gnat's larvae eat roots, causing them to rot so that your plants have problems taking nutrients in. Controlling the flies with sticky paper strips isn't enough, get some Nematodes into the medium to eat the larvae. I don't know what ring tails are, but I'd try to get rid of them too...
DC AC Power Inverters - Frequently Asked Questions has a calculator - You might get an hour of 600w@230v out of a decent fully charged 12v battery with an inverter connected directly to the terminals.
I don't see why you can't cut holes in the sides. Use 2 or 3 inch ABS DWV 90° degree elbows (they're black) from a hardware store, there won't be any light leak or reflection inside. Cut a circle in the box slightly smaller than the elbow and push it through, you might need to put some duct tape...