I have a very old set of Frog Togs ... they kind of look like they are made of Tyvek, I think they may be. The top and bottoms might weigh about a pound total. They fold up to a tiny bag and will fit over anything I wear. there is a zipper on the pants at the bottom that helps get them on over boots and a heat shield on the right leg.
I've worn these in torrential downpours in 80* temps and stayed cool and dry. They aren't much good for real cold, but, I have snow pants and layers of jackets for that. And yes, the frog togs will fit over the snow pants. I also have electric gloves and socks ... I do look like an Umpa Lumpa, but, I'm warm and dry.
I've gone to a layering system because of my locale. I can leave home and the temp is 65*, within an hour I can be in 30* temps with rain or snow, and hour after that, I could be in 80* temps.
I have a light weight jacket (HD) that is water proof, under that I have an electric jacket liner, under that I have a quilted jacket (HD) and/or a mesh jacket (HD), I stay toasty. The outer jacket and the electric liner zip together so you just have one zipper to remove them. I rarely use the quilted liner, but, it's there if I need it. I like to put the mesh jacket under the electric liner, acts like a thermal blanket.
On the bottom I have my riding pants (these are the kind you can unzip the bottom and make them shorts) and if it's cold, my snow pants.
The Frog Togs will fit over all of it.