(Mods: I don't know if I can post this so no hard feelings if you delete it.)
I have no affiliation with this product or seller. I found it on a popular online market place but purchased one and thought I would share. It is a battery holder made to fit in the 8'' twist and go hatch on Hobie. This was the largest size for a 12 and 6 volt battery but I think there are two other sizes available. Anyways it worked well for me, all I did was drill some holes in the bottom so that if water gets in through the hatch it will not collect around the battery. It shifted some weight to the back and gave me a little more room for fish and ice up front. I was happy with it and just wanted to share. Again I have nothing to gain from this but thought it was a useful product since I never store anything in the rear hatch that I may need while out at sea.
Fold the finder down inside when not in use 
Could also use it to store some small Plano boxes for hooks, heads, etc.