We don't attach our FirstUp to our Uhaul
when we set it up as our canopy (really a screen room). We use the plastic rain drip catcher (I don't know the official name for this.) that we put around the top of the door. The metal for the FirstUp sits nicely in this.
We have the awning for our Eurovan that we have not ever used except to try it out. I wonder if it would work. It had some kind of attachment that connected to the rain gutter. We did not need it with the FirstUp. Looks like the same one as used for the VW bus.