Depends on where you want to go. Longmire/Ohanapecosh/La Wis Wis (SE corner of park) are below 2000 ft elevation, so snow is not a problem. Sunrise is somewhat higher elevation, and if you want to go up to Paradise (and everyone does), the road will almost certainly be open but there may still be a lot of snow (or, a LOT of snow). This has been an above average snow year up there so far, so I would camp in the aforementioned SE corner, or if you like private slab campgrounds, in the small town of Packwood. Drive your car up to Paradise, any RV is a bad idea on that road.