[scooter729]

I would actually be more concerned about the front than the back, with E91s.

I've seen (and own) many E91s where the front can chip away easily. The Overall I have here is a good example. Not sure exactly what caused this; these cards were never soaked, but I'm guessing some effect of moisture did it for the ones I have. I know I've seen this with some other E cards as well (E94s, maybe?), but you'll definitely want to be careful about soaking an E91 for that reason.