Hi kimelaine -- the reference is here
(see page 2).
22 = length
D = double bed
6 = 1976
S = *
5356 = 4 digit sequential production number in the 1970s
* S normally
stands for Santa Fe Springs, CA, but I've got to side with Shari. As far as I know Argosy trailers were only built in Versailles, OH, about 30 miles southwest of Jackson Center. Could they have made a mistake in making up the VIN sequence for your Argosy?
On my '74 24' Argosy, the VIN tag is riveted near the front water fill door. The VIN is also embossed on the right side of the A-frame, below and behind the LP tanks.