Thanks for another alternative.

But, we are travelling pretty "heavily", since we'll be taking the RV from Iowa to Florida (different climate zones right there) and then spending a couple of weeks in Florida before doing a 14 night cruise back to Europe. So, lots of packing for those 6 or 7 weeks total.

Have checked out the Greyhound option (not bad at $38 pp with 7 day advance booking) or one-way car rental from Chicago to Des Moines. For the one-way I've found a good possibility with only $100 drop-off charge, making the total about $170 incl. taxes, if I book with our German auto club. Since we would need a taxi from Greyhound to DSM, where the RV company has reserved (and paid for) our hotel overnight etc. etc., we may just go with the car rental -- for the small difference in price. That's all presuming that there is no snowstorm