I would like to add real river rock around a gas insert that I already have. I have a crawl space. What is the best method to reinforce the weight of the new rock work in my crawl space.

That depends on so many things that a simple answer is impossible. Nothing that's installed in the crawl space is going to be easy, though. It could be steel, it could be masonry, but either will require some footing work. One would need to see the existing structure, and know the exact location and dimensions of the new stone, plus the height and weight of it, before anything could be suggested.