Geoffrey,

Several years ago there was a fellow in Tennessee that sold plans, Lubeck I think.
I don't think his plans are still available but I bought a set and used them as a starting point to build two(!) trailers for G103 gliders (I must have been a crazy man!)

The best part about the plans were the sources for special parts like rivets and pre-painted aluminum sheets.

I think there should be a few sets that can be obtained by loan or purchase, they are copyrighted so copying isn't an option.

Mike B.