Another issue about used campers/motorhomes is that you don't know how they were treated or cared for. You don't know if it sat for a long time or if it was driven and never given an oil change or other required maintenance done. There is so much of the unit that you can not see that could be an underlying issue.
If you have cash to buy outright and stick $10k in a repair fund as DaHose mentioned, then it might be worth the gamble. But if you are like most of us are and need to finance, then you probably wouldn't have that large of a repair fund. But if you are gonna spend $25k on a unit and end up having to use that $10k in repairs, then it might be worth to get the $50k unit that is covered under a warranty after the time and headaches of the used unit sitting in a repair shop or you being stranded.