my batts (4-GC2) sit just fwd of the engine under the companionway stairs. The stairs actually form an enclosure over/around the batts. With a new engine going in next month, I'm looking at trying to minimise the off gassing to prevent corrrosion on the engine. Anybody have any experience with vent caps that supposedly do this? Looking the water miser cap. I know hydro caps have around for yrs and were expensive. No prices on their website so they must still be....Oh, and not practical to relocate them..