I was going to try the tire method, but hubby didn't like the idea of tire piles in the yard (veggie garden is on the side of our backyard). Don't know that the boxes looked much better, so I ended up making a row of strawbales, and the boxes sit behind them. I think the tires would have been better because you can stack and add to hill up as you go, and the black rubber gives warmth.
Even though my potatoes were a little shaded down in the box at first, they are growing like gangbusters, even the one in the feed bag. I need to add another "lasagne" layer of straw, newspaper pieces and dirt. I've added & hilled up a few times already, but the leafy tops are at or above the tops of the boxes now.