I´ve got a PAV in my garage. Long term (I mean L O N G!!) project.
The chassis is OK - blasted + painted and the wheel + suspension are also fixed. The trailer body itself is still unpainted and so far not attached to the chassis. Wiring, paint preps + paint are what I have to do. Sometime!
I don´t have any build instructions but can take any picture you may wish of my PAV. There are two varieties of the suspension - one with rubber elements and one with two small shocks. I have the rubber variant.
Maybe I can dig something out from sites I´ve been reading from in the past - must try to remember where they were.
There´s a guy, Jan Månsson, not far from me who makes all sorts of components / spares to these trailers from SS. Maybe you can be helped with a couple of pictures from his site.
I was just curious because my brother was thinking of building one but the suspension element looks the hardest. The rest seems to be a gooseneck with a basic platform on it. If it were on a bicycle it wouldn't need suspension but on a motorcycle i'm pretty sure it's needed.
I also saw a build where a guy took a hardware store dolly and reduced it to one wheel but it didn't look so good.
AFAIK these PAVs didn't come as a kit, so no building instructions. But for pictures of a restoration look here http://www.vanengelenhoven.net/ If you have any questions write to the site owner (Erik), English is OK, and he'll probably be happy to give you answer.
I think you've got it with that last picture. A small spring shock to carry the weight. Key is that mounting to the motorcycle, it needs to be able to turn side to side but not tilt side to side. That means you're not using a ball hitch anymore.