Not only lightweight exotic materials, but using conventional materials more efficiently, in stronger structural shapes.
Sure it can be done, but developing those designs costs money, and building them costs even more.
You're talking about a $25,000 RV in a virtually invisible, unregulated industry compared to a $25,000,000 airplane in a highly visible, heavily regulated industry.
By visible, when a plane crashes and kills 120 people, it makes national news, but when an RV leaks and starts to fall apart, mildly inconveniencing the owner, nobody cares.
