A large LiFePO4 battery inside the coach safety concerns?

I wouldn't have a problem with them under the bed. LifePo4's don't fail spectacularly like LiPo's. When LiPo's fail you end up with a really large fire spewing torch. LifePo4's chemistry is so stable that fire risk is pretty much nonexistent. If you're somehow able to get them to the point of failure, the cell just pops and out gases without fire. There's more of a fire risk from the devices and wires feeding the battery.