Not many choices:
https://www.campgroundreviews.com/regions/alaska/petersburgAre you going this year? Are you touring Alaska? I highly recommend Mike and Terri Church's book, 'Alaskan Camping' which includes Canada, Yukon and the border states of the lower U.S. They lived in Fairbanks and traveled to the lower 48 all the time so they know the campgrounds and boondocking spots.
Due to Covid you may find campgrounds and fuel stations out of business. They've had a tough time staying afloat without travelers. Always drive on the top 1/2 of your tank and don't plan to shop for good prices. Get it when you see it.