The "Towing Signals" could be powering the rear of the coach along with the trailer connector to your toad. The chassis is delivered without rear Stop/Tail/Turn lights, and the MoHo builders often find it easier to use the "Trailer Tow" harness that's provided with the chassis.
So yes, possible that fuse you found is the culprit. Our E450 didn't blow fuses, but the wiring was so skimpy the incandescent lights on the rear of the coach weren't very bright. When I connected incandescent lights for the toad, too dim to be satisfactory. Rather than run better wiring, install relays, etc. I replaced the OEM rear lights on the coach with LED, and installed LED "Trailer" lights on the toad.