It sounds like you don't realize that you can not run metal rods across the grain of solid wood. Wood expands and contracts with changes in relative humidity and must not have anything that will try to stop that movement. If you use threaded rod, and install it during the summer (when the boards have expanded) during the winter the wood will shrink and the rods will be loose. If you then tighten them up, next summer when the wood will again swell, the ends of the rods will be drawn into the wood. At some point during the year, the glued up and rodded panels will warp, split or in some way fail.
A basic woodworking rule is that you should never create a cross grain joint.
If you glue and clamp correctly, your panels should be and remain flat.