Updoing Container pots for edible gardening.

I have plenty of decorative garden pots that I now want to use for a container garden of edible food. The question I have involves paint, sealer and safety issues. For clay pots I used clay pot sealer, outdoor paint and Rustoleum sealer. And it's only now that I am working on a foam garden pot that it occurs to me that I might have sealed the fate of these pots.

So, my questions:

1) Are these painted and sealed pots safe to use for the purpose intended?

2) If yes, what kind of sealers are best for foam style garden pots. This isn't cheap foam, but the kind that is meant to stand up to the elements. It does soak in paint. I did not think of sealing it first, but would like to protect the paint finish from the elements.

Please share your advice and experiences. Thanks.