There are
many Conventional slab sided trailers with a thin layer of
fiberglass as the exterior skin, which often will develop bubbles in that skin with time. . They are not the molded FGRVs as we so enjoy on this forum.
They claim to be super aerodynamic because the have rolled or angled the front a bit more than they used to be. That front still pushes
a lot of air. The sharp cornors create turbulance and = more wind resistance. The flat rear of the trailer creates a vacumn and pulls air along with it, which also affects fuel mileage in a negative way.
The flat sides act as a sail in cross winds and react very negatively when passed by an 18 wheeler.
The tops on most of them tend to leak, especially around the edges where they meet the sides. Water can get between the walls and rot wood and/or cause mold. It can be there for a long time before being detected.
When we were actively camping, years ago, next to the last trailer we owned was an Argosy by Air Stream. It was a dream to tow, compared to the several conventional trailers we had previously. We put a lot of miles on it, behind our Chevy van that was modified for towing.
Because the kids were growing and wanting to bring friends along we traded the Argosy for a Fleetwood "Terry" which was larger and heavier.
We made one trip with it from Atlanta to Orlando Florida. The towing part of that trip was a nightmare, compared to the many miles we towed the Argosy. When we got back home it went on a rented space at a local lake and remained there until we eventually brought it home and
sold it.
All that to say this: For towing and covering a lot of ground, as comfortably as possible, the molded FGRVs are heads and tails above conventional trailers. For "Living", the conventionals offer considerably more room and storage, but more maintenance.
Kip