On Fri, 15 Feb 2008 13:29:43 -0800, cavalamb himself
wrote:

The battery will emit Hydrogen gas when under load.

The box should be gas tight and vented overboard where a stray spark
can't ignite the H2.

It should also be about to hold spilled or leaked acid without leaking
acid into the boat.

About ninty years ago, a US sub had a H2 explosion at the dock.
Eventually the Navy installed proper ventelation. Don't even ask about
the gasoline subs. No venting fumes over the side while submerged..

Casady