The S is sometimes placed before the number as in S550 and I think it means S Klasse = luxury... I found this...
"Hymer S-Class
With the new S-Class, HYMER has produced a Masterpiece. The new automotive design leaves nothing to be desired."
I hope it's true...
http://concorde-motorhomes.com/motorhomes/hymer_motorhomes.php
Peccavi
July 2009