I used a cheap coated nylon athletic suit while winter camping in Michigan's UP many years ago. It kept my bag dry from the inside and seemed to add 5-10 degrees to the bag's warmth.
Recently purchased Stephenson's VB shirt & pants, made from the gray Fuzzy Stuff. Pants are 5 oz, shirt 5.5 oz. I could do without the pocket on the shirt, and a shorter zipper would also be welcome, but they fit and work well. I had planned to go MYOG using Sil, but the AGGs look good for the price and may be a more expedient way to go.
I'm sold on the VB suit for sleeping below freezing. It permits me supplement with additional clothing, which I couldn't do with a simple VB liner, and adding it to my Phantom is still lighter than my old Blue Kazoo down bag.
Thus far I've only slept in my Stephenson suit a few nights. They are not clammy or damp. My MYOG momentum bag cover left me feeling damp, and consequently cold, in temps around 25-30. The suit takes care of that, and seems to add 5 to 10 deg to my Phantom 32.
I recently took that bag down to 5-10 deg F, fairly comfortably, using MYOG cover, the VB suit & socks, base layer & R1 hoodie, Cocoon pants, MB UL 1/2 sleeve down jacket, Puff pullover and Cocoon balaclava.
On a separate night the lows were around 18-22, and I was too warm in a similar setup minus the 1/2 sleeve jacket. Slept with the bag open, not using the hood, until about 0530.
Haven't experimented with wearing it above freezing, but in those conditions my bivy still tends to condense and leave me feeling damp/cold, so will probably try the VB suit some this spring to establish effective upper limits.
These wouldn't vent enough for me underway in the conditions I encounter, but to keep my other layers dry when I'm wearing a pack I plan to make a 2nd layer vest using a sil back and shoulders, momentum face and something porous and stretchy on the sides.