We sailed in June 2021. Booked in Skagway through Temsco, with the same plan you have. I expressed concern about the weather when booking and I believe the rep said they would do what they could to rebook us for Juneau should it come to that. Luckily, it was a beautiful day for us in Skagway so we didn't have to worry about rebooking. The dog sledding is absolutely incredible and worth every single penny. Highlight of the trip for us.