So as it turns out, I was skunked by clouds the entirety of the trip--except for the night I got into town (Tuesday the 18th; I had to stay behind for a few days while my wife went on ahead).
I did get to scout out a few spots that night, though, and got a few SQM readings. We went by the Baker Lake dam, which would've been a decent spot if not for the insanely-bright floodlight there; I got several 21.2 readings (aiming into the Great Square of Pegasus, the best patch of measurable sky available).
Along Baker Lake Road, there are a couple of small hills with bare tops (I labeled them Baker 1 and 2 on the Google Earth shot posted earlier). These were gated off, but stopping by the gate of the #2 spot yielded SQM readings of 21.6.
The Shannon Creek boat launch had potential, but I didn't get to check it out at night. Of course, being so close to the lake was a recipe for heavy dewing, too.
Also along Baker Lake Road is a gravel road off to the west (Schreiber's Meadow Road). The road was closed at the 4.5-mile mark, but there's a gravel pit at 48 40 40 N, 121 43 41 W that had some decent and usable open sky, but the horizons are pretty blocked by trees. Again, I only got there during the day; it seems to be popular with those looking to create empty shell casings.
The Marblemount boat launch was a no-go.
The Hurn Field wildlife-viewing area is usable for observing if you don't mind cars whizzing past on the highway; I got readings of 21.2 and 21.3 there. Nice views to the south.
We drove the Cascade Loop, so went into Mazama, Diablo Lake, and Lake Chelan. Looked like plenty of potential spots there. And also at Artist Point on Mount Baker, but I didn't have time to look for a specific spot there.
Beautiful area, with a lot to do besides astronomy. I'll have to go back once they get the weather machine fixed.