The cheaper ones use a mechanical pendulum to guage how much power to send to the trailer brakes. Not good when going up hills (won't send much power to trailer brakes) or going down hills (will send to much power to trailer brakes).
A Wrangler plus an 18 foot trailer weigh more then your Grand, so you want to make sure your trailer brakes will work as smooth as possible. Sure hope your trailer has brakes on both axles.
A good brand is Tekonsha, and one of their better models is the Prodigy. You can get 'em on eBay for as little as $100. This is the one I have, and love it.