We pulled our fifth wheel over Highway 2 with no problems at all. There are some curvy bits and hills, but we didn't have any trouble. We had an '08 F350 diesel pulling a 12,000lb 34ft 5-er at the time.
It is a 2-lane highway much of the time, so I'd plan it for mid-day weekday (but not Friday) to avoid lots of traffic.
Our 5'er owners group held rallies at
Wenatchee River County Park (we never made it there with them), but that's only 125miles or so from Everett.
The Moses Lake area should have some nice parks to choose from on I90
Grand Coulee Dam or Coulee City also have some good options (include a WA State Park).
https://washington.goingtocamp.com/W...StateParks?Map