Just so you know, it's Idwal not Idwel and Llyn Idwal not Lyn Idwel. "y" is pronounced "uh" and "f"'s are pronounced "v". "Ll" is like an "l" but with a little air allowed to pass round the sides and bottom of your tongue creating a sort of low wet sizzle. Nice huh? No, not really. The locals will be far more welcoming for a bit of correct pronunciation, trust me.
try here
150m north west of the boggy bit around Llyn Y Cwn (accent missing, pronounced "koon") at the top of Devil's Kitchen on the drier area before the slope up to Y Garn starts would be a lovely place to camp.
Hope you have a nice time.