I tried the Hollow core Door thing along time ago and It works for Many things, However I was building a new work Bench myself lately and stumbled onto something i think worked out well for me. I found a solid core Fire Door at Lowes, It had this Formica like sheeting over the entire door. Cost was around $48.00 and she was thick straight and true. Measurement was about 36"x 80" Ran a contractors level over it that i borrowed from a different isle at Lowes, No runs dips or errors.Worked great for me.

Semper Fi