OK, so the Gus isn't a direct battery or hybrid mod.
I'd still be concerned about the tight quarters around the battery, which would prevent the escape of gas to the vent hole in the bottom. It might as well not have any vent holes. You're only safety feature is the fuse, which is probably more than most mechs have.
One thing to check once you get the mod. Blow into the top of the mod, and if you can easily blow air past the battery out through the fire button's hole, you're probably ok.
To drill or not to drill? The choice is yours alone, Zut.