I am ready to replace the top of my workbench with a dead-flat torsion box to ease assembly of future projects.
I built my current workbench a couple of years ago from plans from Fine Woodworking. The base is made by laminating plywood strips and is very solid. I filled the inside of the base with 6 drawers which are full and work very well. The top is 2 sheets of 3/4 material that has served its purpose, but is far from flat.
Part of the reason why the current top is not flat stems from the fact that I have a heavy vice on the left side of the bench. This is mounted on the underside of the top, that is overhanging the base. So, the weight of that vice pulls the top down on the left side, bowing the whole surface.
So – I am going to replace the current top with a dead-flat torsion box. I plan on re-mounting the vice to it, but will add support legs on the other side to help support the vice weight. This bench will become more of an assembly-table, though in the meantime I use it for all workbench purposes.