Renting will cost more than towing your RV on the (very long) 1 day trip, or even an Airbnb.
But that aside, get reservations for camping. Acadia is packed in August.
You may take the Mt Washington cog railway up to the highest summit on the east coast.
You may like something called The Flume
The Cannon Mountain areial team is open to take you to the top of that mountain as well.
In Acadia, a popular thing to do is hike up and see the sunrise. It's the first place the sun touches in the United States each day.
Then there are the islands. Highly recommend taking a ferry out and exploring some of the islands in Maine or at least going on a windjammer cruise. Maine is about the water. And the mountains. They meet each other there in a very special way.
Lighthouses... fresh seafood... Lobster, haddock and cod from local waters
It's a slow, relaxed atmosphere in Maine in the summer. Enjoy the peace.