FM,
In regards to mounting starboard to the inside of a console, if there is enough existing coring to mount the piece, then simply screwing it in place (as Rick mentioned) will do. If there is no coring, then t/bolting is the way to go. #10 oval head machine screws with finish washers under the heads gives a good clean appearance...
Now, in regards to a battery drain, in theory, with the batt switch in the off position, there should only be 2 circuits that are "constant hot", one being the bilge float switch, the other being stereo memory (if you have a stereo). Both of these circuits, once again in theory, should be fused close to the batt switch (within 7", but going a little further won't hurt). Pull the fuses in each of these circuits and see if that stops the drain. There is also the possibility that you have a bad cell in the batt, regardless of it's age. This can be a bit tricky to diagnose, as rest voltage can appear to be normal (12.3 or so), yet as soon as any decent load is put on the batt, the voltage will drop down to less than 10.
What I've noticed in batts with bad cells is that when you put them on a charger, the voltage only increases to around 12.7-12.8, whereas a "good" batt will show around 13.2-13.3 when charging. Once the good batt is fully charged and the charger removed, it should show a rest voltage of around 12.65.
Hope this helps...
