Personally, I didn't want to inherit another person's problems, so I bought new. You never know how a used RV was treated or maintained.
My wife and I went to RV shows where RV's from multiple dealers were in a large field. After attending several shows we found the trailers that we liked best. We didn't really know which dealer was selling a specific trailer, but we knew which ones we liked. When it was time to buy, we visited the dealer selling that model, made a fair deal and went camping. We haven't been back to the dealer since the purchase. If I need help with maintenance I use a mobile RV tech who comes to my house.
