I have heard a few times to take into consideration the water level before loading rafts with meat. We will be out there mid to late august. We have made plans for meat preparation and maintenance in the field hopefully that pays off over the trip. At the headwaters of the charley I don't know how aggressive we will be pursuing animals, unless presented a can't pass up bow shot.Usually.....I'd expect more caribou in the early part of your trip. The 3 Finger Charley are can be quite good. Consider water level before loading rafts with caribou meat too early in the trip. You mention a "summer" trip.
You have a considerable but interesting float ahead of you and meat spoilage could be an issue. There's good grayling fishing as well as dolly varden along the way.