We did a similar time frame trip many years ago, some real whitewater first day on the Tat couple ledgy rapids. Water hard to read. After that pretty easy some wood lots of channel reading easy to get stuck if not on your toes. Good guidebook called The Complete Guide to the Tatshenshini River by Lyman, Ordonez and Speaks. We laid over Walker Glacier and Alsek Lake. You'll want an excellent camera mind boggling scenery. One of the coolest camps is at the confluence with Alsek. Leave some extra time at dry bay flights can be delayed. Have fun it is well worth the drive. I echo the rain gear comment, we had good weather but when it did rain watch out! Also the camera, from the fireweed to the Glaciers it is unbelievable.