Does the park close in winter and if so when? Particularly wanting to know if backpacking / back country camp sites close at a certain point.

Open all winter wont let you backpack in snow unless you are already there

Open every day. Gates close at night but this year they have opened an access road if you need to leave after hours.

The tent/RV sites are open year round. I can't speak to the backpacking sites though. You should be able to call and find out though.

Open all winter i believe

Open all year