The problem is that mirroring the front with the rear is that the settings for the two are different. If there's four wheel steering for any other carsyou have, I'd look into modeling the front/rear suspension after it in the offroad setup.
There is the 4WS pessima but thats designed for better handling on roads rather than rock crawling and it wouldn't have the suspension travel for it either. it's also independent suspension which has some advantages but probably not good for what you'd want. The final problem is that its meant for a front wheel drive car and front wheel drive only.