Hi I searched and couldn't find any trip reports of this trip so I'll write up a quick one for anyone interested in doing it.
Did this trip in mid-September with a friend in a two person kayak. Parked one car at the end of Seton Lake near Lillooet, there's lots of parking near the beach here and I did not see any signs for overnight restrictions. Drove the second car to D'Arcy where we launched from the dock. Again lots of parking in D'Arcy, no signs about parking restrictions.
LOTS of people had warned me about wind on these lakes. As you know, mountains all around can funnel wind like crazy. We generally followed the south side of Anderson and the north side of Seton, there are good pull-out location all along both lakes. Just once on Anderson Lake the wind picked-up, sent choppy white capped waves that smothered the kayak. We had to pull over and wait it out for 3 hours. Seton Lake we encountered a little headwind, but nothing crazy. Like usual, starting early morning seemed to be the play.
Anderson Lake has lots of nice camping along the south side, some permanent spots with picnic tables. Seton Lake had fewer potential camp sites. We still managed to find a nice place to sleep on the north side of Seton. Seton Portage in the middle has a motel and pub for those of you with $$$. There is an official campground in Seton Portage, it appeared to be closed when we were there. I think this area is popular tourist destination in the summer, seemed very quiet by mid-september.
Carrying gear through Seton Portage was pleasant enough. There was a locked gate on the road up from the beach on the Anderson Lake side. We were able to walk around the gate. Lots of work trucks driving through the village, could probably hitch a ride if one was so inclined.
Views from the lakes are great. Still, lots of signs of "civilization" can be seen (power lines, railway tracks, cabins, etc). Saw a couple otters in Seton Lake.
We brought lots of water with us. There were a couple creeks you could fill up along the lakes, but not a ton. I'm sure you could fill up at the pub in Seton Portage as well.
I posted some photos here