If you want to attract people to your OBCZ via release-notes and the "go hunting" pages, you'll need to include enough location info for them to find it - but you don't have to include a specific house address. I've seen OBCZs and Little Free Libraries that only mention a street name, and as long as it isn't a very *long* street that's enough for interested parties to be able to find it, without putting your house number in search-engine-findable form. Your idea for "1800 block of Main St." sounds like a reasonable option - you don't even have to name the side of the street if you plan to post obvious signs at the location. (Mentioning in the OBCZ release-zone page that your OBCZ is a bench, with no visible bookshelves, would be a good idea - a photo would help. Here's the release-zone page for Moem's home-based OBCZ in the Netherlands, as an example:http://www.bookcrossing.com/---/749099
Now, if you're not comfortable with the idea of drawing strangers to your house - even if it's to swap books - maybe you could find some other location for your OBCZ; a nearby park, perhaps, where you could easily keep an eye on the contents.
Note that even if you don't post a street address, someone else who spots the OBCZ might do so; some sites, like LibraryThing, allow people to submit the locations of book-swap shelves like LFLs and OBCZs, so your street address might wind up there anyway. (If you find this out you could ask them to remove it, but you probably couldn't police every site.) I haven't heard of anyone having problems from publishing their street address, but that doesn't mean it hasn't happened - I guess that would mean it's up to you and your comfort-level.