Next time you run across a first-generation Chevy Corvair, take a peek at how they did the hood at the factory.
The entire center of the hood is louvered, but in two layers. Water gets in no matter what, but when it does it's just channeled down and back to drain holes (scuppers?) along the trailing edge and out it goes.
Back then, very little was weather-resistant (much less proof!) like it is today. So water control was more important than perhaps even on our trucks.
Sure, a double-layered panel would increase the price drastically I'm sure. And in the case of the Corvair, it was mostly for cooling and combustion air intake, rather than exit, but at least it's a concept that's valid from a performance standpoint.
Would probably strengthen the whole hood too!
Besides, we should be doing whatever we can to make our Broncos moisture proof anyway.
Paul