I just threw out a catalog that listed a product for shipping/packing stuff. The product was a in a plastic/Mylar bag, and had two poppable plastic bags inside. You take the Mylar bag, place it inside a box, pop the internal bags, knead them to mix, then place the ship unit on top. The contents of the Mylar react to each other and make a foam that becomes rigid, yet soft enough to support without damage.

You know, come to think of it, I had to ship a VW engine case to California for some custom machine work. I found a sizable box, wrapped the case in an industrial garbage bag, then used a can of triple expanding foam insulation to protect the bagged part.
You could probably remove a rectangle of the foam to make a bed big enough for one gun, and a second for the other gun, then make custom beds for each gun using that method.