Proper Maintenance is the key to a high mileage RV,if that is kept up then there should be no problem. Most newer vehicles will go over 200000 miles.
Take for instance
Former Rentals most of not all have more than 100000 miles on them and with the proper maintenance that they get they are going strong with no or very little problems,there are more than 90 owners here that are happy with their RVs.
Try to look for one that you can verify the maintenance on it if you can,don't be afraid of that. All other things being equal.