vintage craft: styrofoam tray looms

After a several-week period of mourning my old, seemingly-deceased scanner, I again have access to one that works. Which means I can bring you more McCall's Creative Handcrafts! This tray-loom idea is from 1969's Annual. 

I love this craft idea and think it looks great today. The main problem with translating it to a 2016-era craft is the relative unavailability of styrofoam trays. I think the last tray I got was at H-Mart, where it was holding a half-dozen Asian pears (so delicious). I am far too paranoid of e coli and salmonella to use a meat-containing tray for crafts. It's been a while since I looked, but my local supermarket used to sell their half-price, over-ripe produce wrapped in styrofoam trays, so that would be a safe way to get some. 
I'm working on a variation of this craft that doesn't use styrofoam at all. In the meantime, here are the directions, beamed to you from way back in 1969.