Holes in the bottom. What are they for?

[TankerIP]

I've got these holes under the bath. I wonder if anyone else has this kind of thing on their trailer. The first is about 10" long, black plastic housing. Possibly related to the bath. Problem is it terminates in a hole to above that is not the same shape and leaves an opening.

The second is just an uncovered hole. The position that it is end makes me think it would be hard to drill this kind of hole with the banana wrap in place. I understand possibly an inspection hole, but should there not be a cover on it?

I would like to compare with someone who has a similar trailer and see what they might have underneath.

[somefun]

Could it be the bathroom exhaust vent hole? I have one in my '74.