Some wall strength also comes from interior structures. In a teardrop, the shelving and divider between sleeping area and kitchen area adds to the structure of the entire box.
But if you are looking at steel tube framed cabin, look at Firemedic's build and also Aspenx build threads here.
As I read your question, I thought about the exterior panels of standard RVs. I've had a chance to see how a couple were made, and if I'm thinking correctly, it seems like they were skinned in 1/4 fiberglass. Can anyone confirm that? 1/4" is flimsy all alone, but I would imagine being backed with steel bracing, and covered with the rigidity of fiberglass, that it wouldn't actually be as flimsy as you would think. Definitely save on weight too. If I wasn't using the skinning that I am, I believe I'd research that route.
Here's how Rpod walls are made:
The exterior product is called
filon, it is a fiberglass sheet that is 1/16" thick. It is very flexible and benefits from a solid backing.
Fiberglass layups for whitewater kayaks are probably less than 1/8" and very rigid. They are also vacuum bagged in a mold and often a composite of glass weave, carbon, and kevlar. So you can get a thin, rigid fiberglass without a solid backing, but it is labor intensive, lots of dangerous and messy chemicals that are also expensive.
There are some cool products out there that can be used for skinning on top of a frame. One that stands out to me is alumalite or ACM. It is two layers of aluminum with corrugated plastic between. Here's a
build on TNTTT but I believe they laminated it to a plywood wall. With a frame that shouldn't be necessary. You could get away with using VHB/UHB tape to apply it to your frame.
If you don't want a frame,
this thread shows a product from carbon core that is pretty cool and could be used without an interior frame. There's at least one other thread here on expo which used that to build a camper.
