I'm butting into this thread only because I was following along and read about people trying to prop boards up, balance on their heads, etc.....
These are the best inventions ever.
Clamp one end of the board in place, swing the other end up and clamp it....get it levelled out with some light taps.....then, while still clamped, drill the screws in to hold it in place. Best invention. Ever.
These are the best inventions ever.

Clamp one end of the board in place, swing the other end up and clamp it....get it levelled out with some light taps.....then, while still clamped, drill the screws in to hold it in place. Best invention. Ever.