You can do quite a lot with a bone stock truck... Just keep it slow and keep the big rocks under your tires/sliders... I am working on getting underbody armor, though... can't hurt.

If you can afford the lockers, that makes it even better because you will generally be able to crawl (idle or very low throttle) over stuff and won't have to use momentum... momentum = damage.

Oh - and removing the sway bars - particularly the front - makes a huge difference in your ability to keep tires on the ground... it's a 0 dollar mod that is very worth it! Just put the front one back ON before driving on the street.