Sounds like you may be close to somethng that we don't have much info on!
It is part of the Freightliner section of the electrical, so Winnebago may have little info on what is in there.
But looking at the labels you have posted, it sounds like they control the rear lights.
Whether they also control the wiring to the trailer connection is a guess!
Are you finding them in this box?
Click this snip to see better!
From what you are seeing on a label, this seems like it DOES feed lights on the rear or lights on the trailer connection.
If ALL the trailer connections are out, it would seem odd to be fuses and they all went out at the same time. That makes testing the voltage at these fuses a good idea.
But a way to try to find what these do is to turn on lights on the RV, and then pull these to see if it kills some of the lights.
Then when you say there are black boxes, it sounds like the small relays that might be used to feed power on to the rear lights???
Can you pull on one and wiggle it out?
If you get it out, it may have a drawing and label on one side. What I might guess at finding is a fuse feeds power to these relays (if they are relays) and then the relay feeds power on toward the trailer!
Somewhere I might expect some type of label to tell which relay does what??
Is there a booklet or manual with the RV for the freightliner part?
Without the complete Winnebago drawings and without any information on the Freightliner wiring, we really don't have much to go on for finding the problem.
Maybe you can hunt and peck to find more but we just don't have enough info!
