Reconsider - what happens if your fan stops working and you lose positive pressure? A box full of hydrogen that won't try to naturally vent out of that floor-level vent.
I'd rethink this. Put the "hydrogen exhaust" vent tubing at the TOP of the enclosure, and have it exit via the roof, or as high on a wall as you can. (placed to avoid getting near those panels too). This way if the fan quits, there is still a natural flow for the lighter-than-air hydrogen to want to escape naturally.
That cramped block-wall space kinda freaks me out, since if this is done improperly, and if the block-wall room is also tightly sealed, well - you get the idea.
I see a fire-extinguisher. Good. Assuming you could actually enter the building to get to it, if things go plasma because wires and connectors have melted together rendering breakers, fuses and so forth useless, I'd also like to see an EASILY ACCESSIBLE pair of INSULATED bolt cutters (wrap and insulate the arms, exposing only the cutting heads) so you can at least chomp through ONE of the battery leads.
I usually leave at least one polarity out in a large loop AWAY from the other, so you can cut just one, and not add to the problem by shorting.
Dramatic? Perhaps so, but hey, if it saves someone from injury, it's well worth it.
