I need to make a flat tabletop worksurface 40" x 96". It will only be supported 3 spots over the 96" length at 6", 48" and 90" from either end. I want to come back and measure it years from now and its still flat. The other criteria is I only have 4" of clearance below the top. Flatness should be what is praticle with an 8' straight edge and feeler gauges. Ideally a maple top that I could put an mdf wear surface on would be great except, I haven't had any luck finding one that size, and the cost of one smaller plus shipping is pretty hefty, $400+. It won't be supporting lots of weight, just the usual woodworking worktop. Ideas?
Phil