Chucker, welcome to TVille and enjoy your stay. A lot of knowledgeable folks here and all you have to do is ask the question. EDPM should work fine for a liner. I grow most of my maters in containers but not in closed systems like earthTainer or growboxes. We have Ray here who designed and developed the earthtainer and is always happy to assist.
You can also purchase growbags which are very inexpensive and normally good for one season. EDPM should last several seasons. Just depends on what you want to do. Smart Pots are new and I'm trying a 10 gal size this year to see how tomatoes grow in them. They are pricey but we will see.
Heres a link to a site that sells growbags and Smart Pots. Ami
http://www.hhydro.com/cgi-bin/hhydro/HYDROPONICS_PARTS.html?pg=Hydroponics%20Parts