Great busy tool for the car

We spend a crazy amount of time in the car which means I am always looking for ways to keep the little busy.  I recently saw a fun puzzle project idea-you hot glue magnets on the back of puzzle pieces and use a cookie tray to keep all the pieces in one place in the car like this:

We tried it this last trip and it did not work out so well. I tried it with the thin puzzle pieces and they seemed to curl and crack. I think this is a wonderful idea if you had thicker pieces and maybe used something other than hot glue. Have any of you tried it? We will try it one more time as I think having puzzles in the car would be time well spent!