Well Jeeps are pretty noisy inside so you want a unit that with some power and speakers to match. Speed sensitive volume control would be nice, but might be hard to find in an aftermarket unit.
If you take the top off, or if you have a soft top, the Jeep is not very secure. So consider a unit with a removable face plate that you can take off and lock up or take with you, essentially rendering the radio useless to anyone looking to pull the body.
Sound bars mounted to the roll bar are a popular way to install speakers that are out of the way.