We leave from (and return to) La Crosse, Wisconsin which is just about where Iowa, Minnesota and Wisconsin meet.
We'll travel 3 days downstream and explore one side of the river and then 4 days upstream while exploring the other side.
The closest big city is probably Minneapolis/St. Paul which is where I will probably fly into and rent a bike. From there, it looks like about a half day's ride down the river to La Crosse.
The double beds are a problem for singles but there's nothing we can do about that. I will try and free up one bed for a single by bringing my tent along, so at least we can squeeze one single on board!
I camped on an island in the Mississippi last summer (near La Crosse). It was awesome!
Cheers,
Darry