Printing on glossy inkjet paper -- 20 cents per sheet -- and ironing the paper onto a clean PB gives an almost perfect transfer of the mirror image as an insulative mask against ferric chloride etching. (I have read that magazine paper also works -- experiment with any claycoated paper or cover stock.
Don't use steel wool to scrub your board, it leaves little scraps that can interfere with etching as they rust. Scotchbrite seems a good solution instead, being nonmetallic. You're scrubbing to degrease so a shot of vinegar or alcohol would help. Wear gloves. Scrub everything bright.
Arclight suggests setting the iron to NUCLEAR for the ironing step. Line up your paper (extra registration steps required for 2-sided boards) and tape it on, then fold back the paper. Preheat the board 30 sec with the iron, flap the paper back, and iron firmly.
Let cool, then soak in water to remove the paper. Pull or roll it off gently at first to make sure it's transferred, which it should be, and rub with a finger to get any excess pulp off. (It shouldn't be too delicate after cooling.)
After mask application, go over it with a nice fresh Sharpie or other resist pen or tool to perform any mask touchup or fix any dropout spots.
Soak the board upside-down a few minutes in warm ferric chloride etching solution. Do this on paper, in the dirty side of the shop, with nitrile gloves and a nonmetallic tray and tools. FC eats all kinds of metals, including your aluminum camera and laptop, it stains absolutely everything -- skin, cloth, tile, cement, metal, etc -- and it is a real stinking mess if you spill it.
Remove the board and neutralize any excess FC with baking soda, then rinse in cold water. Baking soda is a shop staple for many reasons as well as neutralizing acids and removing funky odors from the shop fridge.
That's all that's required to make totally serviceable 2-sided boards.