I’m stumped. I thought the trailer in my kit would be an Iron Eagle tiny house trailer, which comes with flanges on the wheel wells for flashing. This is a pretty big deal in a spot that can attract water and send it under the sheathing to do damage. A flange helps very much the way it does in window installations.
The trailer turned out to be a Pac West trailer, and they do not do the flanges.
I really don’t know how I’m going to seal up this area.