I built the same bench the OP is wanting to build about a year and a half ago. It sits in my unheated/uncooled garage in TX and hasn't gone out of flat yet. I'm sure it will happen but at that point I will have outgrown this bench and made a big boy bench. I've been happy with mine so far. As far as the top being flush with the front, if I need a clamp in that area I just grab the bottom of the 2x4. Don't plan on using a holdfast with this bench top, I believe its not deep enough and the action of setting it will destroy your dog holes. I wish I had made my top longer in case I want to add a tail vise at some point. The good thing is, with one sheet of MDF I can make a new top any time I want in about 30 minutes...