A sandwich constructed 1 ply balsa 1ply is very strong and light indeed. I don't use 1/8" thick light ply in any of my design or builds I use 3/32" thick basswood plywood from Aircraft Spruce & Specialty, it is almost as light as light ply with just about the same strength as Birch plywood, this allows me to place all kinds of lightening holes throughout the fuse and achieve the lightest construction of all.
Bob