For my last dummy, rather than binding, or folding in half, or stapling whatever, I took apart an ITOYA 8.5" x 11" portfolio. I took the clear sleeves apart from the black plastic cover. Then I inserted the individual sketches. And dps' are(were) simply two singles facing each other. That way if there were changes, it wouldn't be such a big deal to re-do the dummy. The only drawback is that it must be portrait. I wish I could find a landscape version of such a portfolio.
And I can scan at home rather than xerox at a copy center.