Quite a bit of additional information can be had about Bannerman's Island Arsenal form KABAR2's personal experience. Even I have been there and put in my 2 cents worth in the Second "What is it? Where is it Contest?" in the winter of 2008. I'll post the Tie-Breaker photo for that fun Contest soon.
Here is the link for those who might be interested:
http://www.gboreloaded.com/forums/index.php/topic,136427.30.htmlTracy
Taken from the east bank of the Hudson River, south of Bannerman's Island Arsenal, you can see the Castle arms and armor storage building and also the house he built for family visits, to the left in the trees.