I really wanted a 2-piece couch tray so that the fin/anchor portion could stay in place if I wanted to easily remove the tray portion.

PLA will work just fine for this.

The magnets I used have a diameter of 17.7mm and a thickness of ~3mm. The magnets snap into the pockets and are held tightly. However, I did end up using some double stick tape to shim up the magnets for better magnetic contact. I would also recommend stronger magnets than the ones I provided in the link below.

Here are the magnets I used:

DIYMAG 90Pcs Magnetic Adhesive Dots for Crafts 0.7 * 0.12inch Strong Ceramic Magnets with Adhesives Backing Small Round Button Magnet Dot Heavy Duty Double Sided for Refrigerator Fridge School: Amazon.com: Industrial & Scientific

This is only my second time trying to design, so I hope this is as useful to someone else as it has been for me!

Feedback is appreciated.