just thinking "out loud" but it sure looks to me like someone had a wire routed that way.
I've seen where some folks will route a wire (for solar, an antenna, or whatever) down through the vent, and then pass the wire out of the vent someplace lower (inside the wall or under the coach but above the liquid level)
That hole sure looks about right for a coax cable, complete with residual caulk that used to seal up the hole...
I'd dig all that loose caulk off...from around the hole and also down at the roof membrane... clean it all up and re caulk that....
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