Open every cabinet, with flashlight in hand to examine for water damage. Look for signs of recent painting of any surface, especially around any roof opening (skylight, AC, Antenna). And it may seem strange, sniff everywhere, often problems can be covered to hide visable trouble, but odors are harder to hide unless they are masking them with some spray, which is also an indicator.
If the belly is not enclosed look at the plumbing lines, any changes in materials, color? It could indicate an old failure to winterize and a spring disaster.
The Jayco line has a strong following and most of their products seem well received. Do Your diligence, and make the best call you can.