Regardless of whether the governors say it's OK, I would take into account the specific situation at your marina. If you can walk from the parking lot straight to your boat (and back) without encountering a soul or touching stuff, that is different from a facility laid out where encountering other people may be hard to avoid. Being out is not the issue as such. Encountering other people (or virus they may have left behind) as well as leaving behind virus (if you are unknowingly a carrier) is the issue.Both of the governors of Virginia and Maryland stated several types of outdoor recreational facilities may remain open, including marinas. If they -- with the advice they have available -- say this is OK I'm guessing that going to the marina is OK.
At my marina it is easy to go from my boat to the parking lot and back without encounting anyone. Therefore, I have no problem going to my boat. It would also be easy to use the marina restroom, but that's something I think unwise. Who knows who may have been in there 5 minutes before I arrived? Furthermore, if despite being utterly asymptomatic I am actually infected (and none of us knows this for certain without a test), I don't want to leave any gifts behind in the restroom for anyone else. It's not just about protecting myself but about protecting others as well.
My boat has everything I need aboard anyway, so other than the trip to and from the parking lot (i.e., when the docks are empty, as they mostly are now), I see no reason for particular concern. I'll just stay aboard for as long as I'm down here.