As a follow up to this, the "civilian vehicle flat 4 to military trailer 12 PIN adapter" linked to above works. I plug it into the four way that is on my 90 and then connect it to the NATO socket on my Sankey. It is heavy, especially with the NATO plug on the trailer side, so all of that "kit" stays firmly attached to the trailer and then the lighter 4-way wiring (like an AB kit or similar) is attached to it and has some slack in it for turning, etc... Kind of an expensive option but works.