As I have posted before, when installing a propane/ac frig, always enclose both sides and back if necessary with metal. i have bought many vehicles at salvage sales over the past 25 years, and have seen many burned rv's with the frig as the cause. None that i have seen have ever had a steel casing around the frig.
Multiple fire extinguishers in the bus are also a very good idea. like in the front, in kitchen by frig, in bedroom, in engine bay, in compartments.
and not least of all, smoke n carbon monoxide, etc moniters.
I had house frig's in my last 4 busses, and i have a large propane/ac frig in the current one that is enclosed in metal, and i have somewhere around 8 equipment fire extingushers. If I do have a frig fire, i think i can put it out...
if not, there are always more school and coach busses for sale cheap now...