I use an old nylon sleeping bag liner, that looks like a bivvy but is not waterproof, but works a bit like a VBL.
The main purpose is to Keep the bag clean and add a few degrees to the bag in cold nights.
When I use it outside the bag, the bag will be damp in the morning.
When I use it inside the bag, I will feel damp, but the bag will be dry in the morning.