Most manufacturers don't tell you how they are made, with what materials they are made, what size and distance between studs, etc. I find that to be troubling. I bought a Jayco, because they tell you exactly how they build it. You know what you are getting with them. Lots of the other brands/models I considered, I couldn't find any details at all...
Lighter weight clearly means that they use lighter and/or less components. If it's light and expensive, it might mean they are using lighter components that are strong enough. If it's light and cheap, they are using smaller size studs, leaving more room between them, using thinner plywood on the floor and ceiling, the cabinets are likely thinner and cheaper and the seats/couch/bed/dinette are likely thinner and cheaper too.
Best way to figure it out is to go to RV shows and start narrowing it down that way. I had initially found a whole bunch of floor plans I liked... then went to RV shows and saw how cheap and flimsy some of those makes/models were. I quickly removed them from my list of potential purchases.
