Buying Used C

I am a single woman, going on a long crosscountry trip for most of the next year. I am experienced rver. I am thinking that I will temporarily downsize to a Class C for mileage and parking. 22-24' rv's are pretty scarce and the later models are more than I want to pay (also lots higher than NADA guide). I am finding Cruise America rentals that have been inspected (repaired), have a limited warrantee and I am told are up to the task. Of course, in most instances the mileage is over 120,000. I want to spend $20K or less. I would also like to be able to sell this Class C after the trip is over and not lose too much. Would I be better off to buy a newer (rental) with high mileage or a much older rv with less mileage? What would you advise? Thanks.