Yes- I think that is it-
You can get a box for like .99 cents at the grocery store- I just dump a good amount in the bottom of a plastic bin and seal everyone all up hanging out on the soda for a while (I used this method for some stinky dolls from Peru)
The smell might also just fade on its own- You could also just leave the box of baking soda- opened- in your box storing the ponies. Lots of people do that to soak up nasty smells in their freezers and fridges.