Well, I'm assuming it would not be functional, because I don't think rubber bands will be nearly strong enough to resist forces that would tend to bend the wings. I used Berkeley Fire Wire 50 lb test fishing line connected with clevises, but in a cartwheel a couple of those broke under the strain. I assume they protected the structure from the initial shock before they broke, but I don't know what would have happened without them, or with rubber bands.
I would say that the designer had things very thoroughly worked out, and if he shows rubber bands then they must be OK. They may not do much structurally, but they would be relatively easy to set up, and if Vern Krehbiel said the plane was strong enough that way then I'm sure it is.
Jim