They aren't certified, shouldn't be placed where temp gets above 200F and are not intended to replace fire extinguishers.
I certainly wouldn't put one under a hood. I could understand where passive in a room may give a feeling of security when away from your coach, their FAQs say they are activated by being IN a flame. Meaning if mounted near an RV ceiling, until the flames get that high, they won't do anything. In MY mind, your RV is already totaled by the time the flames get that high.
I would be interested in seeing what others think.