I redeem quite a few miles for my AK trips (2-4 per year) and generally have very good success, even in the summer. I start looking early though and keep looking if a good connection/deal doesn't show up right away. Generally I use NW miles but when I want to make stops in Alaska en route, DL or AA miles are great because they allow that for no additional mileage charge.

If you are flexible, keep checking. I got tickets relatively last minute last summer to FAI with NW. Remember partners and often you must call since the online availability searches don't always turn up all the options.

John