I'm not local to Des Moines, but have been in there a few times. Ankeny is pretty close. Of course, you can land at DSM and use the FBO there.
You can stop way up in Ames and get a rental car.
At Boone, there is an RV build center and I imagine you can get a rental car there.
If you get a chance and have the time, I strongly recommend stopping by Greenfield airport and checking out their excellent museum, but it's a ways to Des Moines.
If it was me, I'd go to Ankeny, but by all means see what others say and make your choice.