Heres something I recently put together to keep my battery box from sliding around.
I gooped some of that stuff you line your drawers with to the bottom of the box for grip.
After I figured out where I wanted the box to sit, I roughed up the bottom of 2 pad eye's and the inside of the hull. I gooped a pad eye on each side of where the box will be situated........Yes, gooped. It's actually quite strong.
I sized up a piece of 1/4" bungee cord and put a open hook on each end. I tried the other type of hook with the locking tab and they are damn near impossible to unhook.
Tadaaaa, it sits in there nice and tight.
