Take a look here
Using a gyro to drive straight This tweaks the rotation input to your drive subroutine. It works with holonomic and skid steer drive methods, and implements a simple P-control. We have used it many times. While the PIDControl subsystem is a great tool to learn how to use ( and you should make it your friend
). It isn't required in this case.
These yaw rate sensors work with the coriolis effect, and can be placed anywhere. Just keep it in the x-y plane of the chassis. Or in your case r, theta
Eric