I've found something . . . And yes Mike, more specifically, I was thinking there's no difference between the application in my picture and an enclosed, ventilated crawl space. HOWEVER, per APA's "Finishing Exposure 1 OSB Sheathing" bulletin, it's not recommended that OSB be used as underlayment for elastomeric coatings. I wasn't expecting that. In all the APA docs I reviewed, there's very little reference to exterior applications for OSB. When discussing OSB on the outside, the only examples ever mentioned are using the product to enclose soffits; not decks, or stairs, or the underside of wall bump-outs (think gas fireplaces.)