I got this idea from a mexican luthier that builds F-style mandolins. Rubber bands aren't really the ideal clamp but they sure seem to do the job just fin on small instruments. Im using a C clamp and a binding clamp & caul to firmly clamp the sound board to the neck and tail block. The white thing underneath this contraption is a delrin cutting board that is rubber banded to the other side of the uke so the rubber-bands clamping the top down don't force it through the mold. The delrin is also magically glue resistant so it keeps my bench clean.