I've researched a bit on this since my bucket list is to see all of our National Parks and Alaska has a few of the most beautiful ones.
Everywhere I asked would discourage me even if what I intend to rent would have 4-wheel drive. They would say, some are truckers, that the roads are touch and go even in summer (roads become soft and slushy since portions are gravel over permafrost).
The best recommendation so far as I remember is to take the ferry and rent the RV from the port town/city and proceed if the locals says conditions are ideal for the road trip to the chosen national park.