I did a Princess Lodges rail tour that was completely separate from my cruise and loved it. There was no bus travel nor were there lots of organized group excursions or planned meals. We could pick the excursions we wanted at each lodge or book something on our own. To me it was the best of all worlds - hotels, train tickets and transfers arranged, leave luggage outside your door each departure morning and find it in your room at the next destination but spend each day as you wish. To me, traveling every leg by train was way better than doing half by bus on a land tour.
https://www.princesslodges.com/alaska-rail-tours/learn/
i chose this unescorted 6 night tour from Fairbanks to Anchorage and would highly recommend it.
https://www.princesslodges.com/alaska-tours/itinerary-3ts/?from_search_query=dG91clR5cGU9ZXhwbG9yZXImc2VhcmNoT25seT0w#3TS