Just sprinkle a couple of tablespoons evenly over the base every couple of weeks, enough to keep it moist but not soaking!
Ooh, are you storing them upside down? You should be, and you should be feeding the brandy through the base too (it soaks it up better than the top which has the crust, *sorry to sound a bit over the top with instructions*). This will also make the top nice and flat as well. They should be sitting on greaseproof paper if you can get it as well. Enjoy!