Well, if the downstairs bathroom has only a toilet and sink, it's not like you can shower there, so keeping all of your stuff upstairs really shouldn't be a big deal, since it's not like you can't sneak your toothbrush down there for when you want to brush your teeth down there.
This is assuming of course that the other guys aren't so dumb as to think that none of you will ever use the downstairs toilet to care of your "business."