Cultured housie / Seattle denizen here:
All points are above are pretty valid. You won't sleep well down in Rainier Beach. Georgetown might have been a peaceful night in the past but most everything in the ID and surrounding is more sketch than it used to be. If you're unfamiliar, the Jungle was/is one of most notorious camps in the city, and after some massive sweeps in 2020 there's a bit of diaspora in the general area surrounding the ID, Beacon Hill, SODO.
If you're going to stay in Seattle proper, stay north of Lake Union: Ballard, Fremont, Wallingford, with a few blocks of buffer zone from Aurora in either direction.
Fremont will have spots, possible knocks from cops or civilians.
Ballard is doable, just know that staying near that Fred Meyer is ruined by long-term RV tenants. There used to be about 30 of them surrounding it, and now all of the street parking is lined with barricades, heavy security. If you rack don't even bother there. You need to ask for a key to get duct tape ffs. There's some more parking in the more industrial areas of Ballard, but there will be cops.
Wallingford is the weird answer. I'm living on the cusp of Fremont and Wallingford, and Wallingford is all old rich folk and tech bros. Nobody will blink at an overnight van. There's a park with bathrooms in the middle of Wallingford, and they've "pedestrianized" some of the streets around it. "Pedestrianized" in quotes because some of these rich folks have just kept the barriers up from the COVID lockdown. Vans drive around the barriers and park there all the time, just don't make a ruckus.
I would be wary of standing out if you parked too close to the water though - that area has private security around the nicer stores / gym where all of the climbing wankers hang out, and further down are the Google and Adobe campuses with 24/7 security.
Parking map for fun. Green is your friend and, like all friends, subject to change.
seattlecitygis.maps.arcgis.com
The 62 runs in and out, goes right by the Vera Project. Not the sketchiest line in the city, but I hear it can be a fentwagon from time to time. Ironically, the sketchiest I've seen it was somebody trying to follow me home from the Vera Project. Last rides are midnight runs over the second most popular suicide bridge in the country.
General rule thumb for all of this is have a buffer zone between yourself and Aurora and you'll be fine up north. Hope this helps any that find it.
And the only reason I made an account after all these years of lurking is to say "Fuck Dick's".