Yes, you need them on kayaks, canoes, and inflatables over 10 ft. Only inflatables under 10 ft. are exempt.
I can't remember the site off hand, but you can Google Idaho Invasive Species stickers. It's an Idaho Recreation website I think, and you can order the stickers online. They were $7 last year.
We do the Snake below Palisades quite a bit. Good camping, great fly fishing, moving water with no real rapids. You must carry a groover & firepan. You can launch at several spots , but you have to stop a Conant to register for your campsite(free). Plus you need a Southfork parking pass to park at the put-in/take-outs. Southfork Outfitters does shuttles. They are located right at the Conant put-in. We do Conant to Byington mostly, but sometimes launch up river towards the dam. Camping above Conant is sparse.