We were just there last weekend and going back next weekend. Lone Fir Resort is the closest RV resort, it's a short 10 mile drive to the ape caves parking lot. There's another one right before it called Cougar RV Park.
The only road really even open is the straight shot to the caves and yes you need a SnoPark Pass which is $22 a day or $42 for the season. There's a deli market in Cougar across the street from the RV parks that sell the passes. They did have rangers on snowmobiles monitoring the parking lots lol.
There's a TON of snow up there

it's all clear roads until a mile before the caves and then it's just instant snow. There was no low level snow last weekend.