RE: How to get a perfectly flat (=plan, leveled) workbench?
I built a base something similar to what Minnflyer is showing. Used a hollow core door for the top. Used threaded inserts in the legs and screwed in locking rubber castor wheels. Put a shelf on the bottom for storing a kit box or arf box while I'm working on it, extra balsa, ply etc. The castor wheels were the most expensive part but well worth it. It is handy to be able to move the table around easily and the wheels are adjustable so leveling is a breeze.
wcb