Drivers of small trucks.....less than 26000 GVWR (gross vehicle weight rating).....over here in the US, don't need a commercial drivers license. That means that the driver doesn't have to keep a log book, and can drive as many hours as they want to. Expedited freight trucks usually fall in this category, and haul cargo that is time sensitive.....medical supples, etc. My first cousin and his wife drove an expedited freight truck for several years as team drivers. One would drive while the other one slept in the sleeper. They hauled mainly explosive ordinance for the government, art, and medical supplies.
The roll up sides would facilitate loading and unloading from the side. In a long enclosed freight trailer, if there is more than one delivery, the cargo must be loaded in reverse order of it being unloaded. .....the cargo for the first stop at the rear of the trailer, and that for the last stop put at the front of the trailer. If,for some, reason, the delivery sequence were to be changed, the cargo has to be moved around. The majority of truck freight is on pallets, which can sit two wide in a truck. By being able to access them from the side, it wouldn't matter what order they were loaded in.
2017 Jason Wolverton spruce/maple, 640, "Luz Blanca"
2016 Kenny Hill New World Estudio 640, cedar
2015 Kenny Hill Performance 640, C/IR
2017 Kenny Hill Player Cutaway, 640, Sp