Do you burn if you walk through a player made campfire? If so, that is an excellent idea! Two at the roof entrance would be perfect. Maybe even two where the path comes out of the tunnel to keep them from coming up close stealthed to spy.
As a caster, if for some reason I am turtled / defending / healing a flag carrier I put down a camp fire just to help with regen A LITTLE. +4 spirit is not much, but it is a tiny edge that might be the difference between OOM and -1- final cast.