I both drilled and added fans.. HOWEVER I worry about dirt and insects.. SO... Read on.
ONe hole is 4" with fan (Exhaust) it blows into the "Gap" between two basement compartments.. Well before I inserted the screws I shoved an automotive air filter , a round one,, the same "Height" as the gap was wide.. The screws keep it from falling out and exposing any part of the hole and it's proof against stuff I don't want in there.
The other hole is behind the Inverter.. On this one I put 4 Long bolts just outside the hole circle. a 2nd air filter fits over the bolts and nuts, and a piece of plywood thegoes on and is nutted down.
Imagine if you will an "Air Filter Sandwich" with the compartment wall being one slice of bread, the plywood the other and the filter the "Filling".
No dirt, no bugs, no problems.
