The sprinter would make a nice motorhome. You might consider a slightly larger dual rear wheel with a sprinter front end, they get wonderful mileage, and are tiny to park in a grocery store parking lot.
I found that when I had a truck camper or a 27' class C, I did not need a car to go sightseeing. Though I take along my Ford Edge or Manx dune buggy all the time now.
I just think that a Sprinter Van would not be nearly large enough to full time in for a couple of weeks. No place to store a week's worth of clothes, and not much space for food, the water capacity is limited to about 12 gallons, hardly enough to drink, let alone take a shower daily for a weekend. Refrigerator is limited to about 5 cubic feet.
Sure it is possible to rent a car in a larger town. But say you will be in Yosemite area for a week. You would need to rent the car in Fresno, and then drive back to the campground. Small towns just don't have a lot of rental cars.
Most National Parks do not have rental cars, I have never seen one. I tried to rent a car in Mesquite NV when my truck broke down there. One casino had 2 cars, both had been rented out that day. I ended up hitching a ride to Las Vegas and renting a car there (the company tow truck was going there).
Good luck!
Fred.