The rain would soak through , don't quite understand why you don't want to use a waterproof turnout rug . We are still using a snuggy hood sweetitch rug under our turnout rug with neck cover as there are still some midge and he rubs if bitten
I wouldn't. Just Nixwax the Snuggy Hood and use your turnout combo on top of it. That's what I'm doing and it's working fine. She's happy living out in the vilest of weather (and she's CLEAN!!).