Start early on your entry day. Went to Duncan last year with my wife and two young sons. Friday in Late August. Permit zeros across the board. We were nervous. Made the decision to hit the water very early, and four Duncan sites were clearing out as we entered. People exiting or just moving to new territory. Generally, availability is a toss up, but entering early can pay off.
If you must camp on Partridge, be aware that 2 of the sites have very little shade if any and the third is at the far end from the Duncan portage and would be proud to take a 2 rating if offered. I did rate it a 2, because less would put in the same status as the other two and that would be too low.
Duncan is a really popular EP. However, most of that traffic is just daytrippers but, Duncan can still fill up. There's no way to predict campsite availability. I think the site nearest the portage to Partridge Lake portage gets overlooked some. It's not a great site but, will work for smaller groups.
Also, if Duncan is filled up, Moss lake is a fairly easy portage away and you could see the campsite there from the end of the portage so, you wouldn't have to commit hauling everything across until verifying that site is available.
Another option, in which I'll all but guaranteed availabilty, is Partridge Lake. There are 3 lower quality sites located there, which is also just one portage away. However, the portage is fairly challenging and may be more than you're up for?
For more detailed information; check out our trip report from last summer. Duncan Lake trip report
Hoping to get thoughts on base camping on Duncan over Labor Day. I will be going in with my young sons and their grandparents, so we are hoping for a relatively easy trip with nice day trip options from the base camp. Duncan looks like a good option with Rose Falls nearby and a few other lakes just one portage away to check out. My question is - there are only 7 sites on this lake. It is pretty close to the entry point. I am concerned we'll get into Duncan and not find a site. Can you share your experience finding sites on Duncan? Does the day of week that we arrive matter much? Thanks