My experience with ERC is you dont have to back it, but you need to make sure the back is really nice. Any knots of those craters it can have can be disasterous.
I sinew backed one and it must be 50-55# @26" and 64" long. holds 1" reflex and has been shot quite a bit. I wouod go with rawhide unless you have alot of time to get rid of sinew backing.
Good luck, I love ERC, shapes so easily it makes me hate the hardwoods sometimes.