Per Arfa Daily:
The curtain-siders (it's not
really 'cloth' - more of a *very* tough plasticised tarp) are used for the
most part for the special purpose of 'palletized deliveries' which is maybe
something that's not done in the U.S. ??

I've seen trailers like that in the USA. Never had a clue as to
their function, though - and I don't know what was inside (i.e.
if the cargo was palletized).
--
Pete Cresswell