I personally would not recommend taking a rental RV on the Denali Highway and it may be restricted from the Chitina-McCarthy road. Probably the only AMHS ferry that you will have time for on a trip that short would be the Whittier-Valdez route. But that ferry would save you a day or more of driving time, so may well be worth it on your schedule.
If you really want to add Glacier Bay, Skagway, or Juneau to your limited schedule, you can fly Alaska Airlines from Anchorage to Juneau and take the AMHS ferry to Skagway or a small boat tour to Glacier Bay. We did that on one trip to Alaska and also added an overnight ferry trip from Skagway to Sitka.
I agree with others that the southern Anchorage-Seward-Kenai-Homer loop and the northern Anchorage-Denali NP-Fairbanks-Delta Junction-Valdez loop are about all you will have time for if you are flying up and renting an RV for a month. But that will give you an overview of the most populous part of the state and you can plan another, future trip to visit the Alaska Panhandle, Kodiak, Haines, Whitehorse, Dawson, etc.
After all, does anyone ever go to Alaska just once?