Hi tsweez,
Nice job.
You may need to add (weld?) a bracket under the entire storage cabinet. The compartment was not designed for that amount of weight. It would not be nice to have the batteries detach from the RV while trundling down the road.
I "hid" my air vent on the rear side of the compartment and used a sponge to keep dust and dirt out. That let me put the vent up a bit higher than if I had gone through the door. I'd suggest covering the "back side" of your vent with some thin sponge to keep out dirt as well.
