Yep, there's lots of folks out there with similar motor homes that don't know they've got a separate set of fuses for that trailer plug. It took me a while to find them on our coach, an '04 Itasca Horizon 36GD with the C-7 330HP CAT. I finally found them, inside the rear, drivers side louvered panel, (the one for the dash A/C in our style coaches). When I did get to them, they were insanely hard to get to and service if needed.
So, I tore that entire area apart and re-located that fuse box so I'd have much better access to it, if and when needed. The first picture below shows what it looked like when I found it. The second one is how it looked when I got done with that arrangement.