Paul I have to get a better photo for you but inside the tank I have a new piece of wide and flat timber constructed as a right angle with one part secured to the bottom of the hull (on the tank stingers) and one part screwed to the transom (the rudder pintle stiffener). Then I screwed little blocks here there and everywhere and the battery slides in and cannot move up down forward or back. A bolt stops it from sliding out the way it went in.....bit hard to explain.
Dodgy sketch attached.

Jason