Upgrading rear brakes - ditch the drums!

I suggest to anyone contemplating this to do their own homework. Download the service manual in order to understand exactly how the system works. It is one of the most complicated braking systems that you can have in a car. It has all the potential for a rathole nightmare. See below for a couple of basic system diagrams.

It would be far easier and cheaper to put an electric brake axle in your trailer.

 

Okay, now the OP's request makes sense. The brakes in a Prius are designed for just the Prius, and that is reasonable since the Prius is not rated for towing.

As Seilerts points out, the Prius braking system is complex in the extreme. Trailer brakes make much more sense. They are easier to install and will provide more control.

Tom