mounting second battery

going to add a second battery to my 02 X-star. I want to put it right next to the other one in the cubby under passengers seat. The one there now is recessed into the floor about 5 inches. I would like to do the same with the other if possible. Would this be a hard task? Can it be done? Is there enough depth/room towards the bow of the current battery to do this. What about getting an identical battery tray to the one that came with the boat? Check with the dealer or is there somewhere local to pick one up? Just trying to make it a clean looking install. Thanks.