David, from your photo of the nest in your caboose, it looks more like a mud wasp nest than the paper wasps:
Mud wasp nest:
and the mud wasp:
paper wasp nest:
and paper wasp:
Mud wasp nests are usually made inside, like in old attics or barns. I'm pretty familiar with them from the attic at the old farmhouse where I grew up, and where my dad's trains were stored. I've had to clean the mud wasp nests out of some of his old tinplate trains as well. The nests are literally made of mud, now dried and hard, and will crumble off if you crunch them; a moist cloth or sponge will wipe away the residue.
The mud wasps are not at all as viscious as the paper wasps. The mud wasps would kind of float around the attic and not bother us. Paper wasps are deadly.