Having had 3 fires in the doghouse of my families old Chevy Van back in the day (2 electrical, 1 leaky carb). And having my parents RV burn to the ground on the side of the freeway, I am a bit more nervous about fires than most.
From my parent RV experience, the time from them realizing they were on fire driving down the road (because the engine started to run funny), and pulling off to the side of the freeway. They had very little time to exit the RV before it was fully engulfed. A highway worker crossing an overpass had spotted them trailing smoke going down the freeway and had called the fire department and got on the freeway to chase after them. So the fire department had a heads up a couple of minutes before most scenarios would have. The fire department basically showed up in time to spray the back wall of the RV to try save the tow vehicle.
So lessons learned from their bad experience... Keep a spare set of keys for the tow car and the hitch assembly hidden on the tow car. While taking your wallet out of your back pocket while driving is good for you back/posture, but you need to keep it on your person somewhere otherwise in addition to having only the clothes on your back, you also don't have any id or credit cards. Use a little portable firesafe to store anything important in your RV that you might need after a fire. The fire Department will happily give it a wack with an axe to open it when they dig it out of what is left of the RV afterwards. For those with regular homes, your RV contents will probably be covered by your homeowners insurance. But it is very helpful to have pictures, description, or even estimates of value of the items in your RV, especially jewelry. Using your cell phone to just take a quick video of you walking around your RV before taking off on a trip can be useful when dealing with the insurance company.
So having a dedicated fire suppression system that directly vents into your problem area in your rig is probably smart idea. You may get burned, or just make the fire worse if you attempt to open the dog house to use a hand held extinguisher.
From the experience with the Van fires, can you easily turn off all the power quickly (for electrical fires). For a small engine compartment fire, can you put it out without destroying your engine? For the small fires, I now carry small Halon handheld fire extinguisher in my classic cars for this reason. As a note, they aren't legal to purchase anymore except to the aviation community. But you can put out a small fuel or electrical fire without residue or damage to most things if you catch it in time.
