For a deeper look into the pros and cons of renovating versus buying new, check out this discussion from experienced full-time RVers:
Before buying, a professional "Level 2" inspection is highly recommended. At a minimum, you should check the roof for leaks, the floors for soft spots, and all electrical and plumbing systems. buying an old rv
Older RVs typically have simpler systems, making them great candidates for renovations and customizations. However, parts for very old appliances may be difficult to find, sometimes requiring a full replacement of the unit. For a deeper look into the pros and