the eel would eventually be cramped, and the 30gal might not work for the life of the eel. I am sure there are bigger SF eels, but the longest I have encountered through talking to people is approximately 29 inches. and when you go 1 - 1.5 inches per gal it gets kinda iffy and cramped. Typically SFEs will hide under your rocks, but on occasion they will stretch out and swim around the tank.
If your are going to go through with it, I would have a pretty substantial clean up crew with nassarious (sp?) snails, different types of hermits, plenty of LR and a small protein skimmer. you will want to keep your water as clean as you can, because in that small of a tank with a messy eater like the eel you don't want your levels to sky rocket.
-prk543