Lol I know this sounds strange - but....

I want to make 4 sides (about 15" tall) to my 16x7' trailer, which
currently has a 6" steel side wall. I want it to carry mulch and
driveway rock gravel.

So, what I really want is a single hinged rectangle that folds up to
16' max, with one corner only to join together to fix it in place. I
can get three sides to fold in on each other flat, but I can't work out
how to do the last side. Need some special type of hinge or something,
I am not sure.

All help welcomed!

Thanks

Dean