amp installing. . .

basically you ideally would have a block that would put two grounds into one point in your chassis,but grounding at two points should be fine if you keep your grounds as short as possible,use the same guage wire as your power wire from the battery ,and use your own ground.  Dont share with anything else ie(brake ground,abs,anything). YOu will want to clean off all paint from your surface make nice and clean and shiny before bolting down your ground you want the least amount of resistance as possible here to avoid a problem later. And if you do all that you should be fine, also make sure you get a good spot for your ground think like this when chosing grounds,your cars chassis is one huge wire it transfers all the negative voltage back to the battery so the clearest point to the battery is best, an example is not using secondary metal that is not directly the same metal as  the batterys ground is on. Now i undersatnd you will not usually be able to get this. for example a bad choice of a ground would be a wheel well,a  piece of metal bolted to the chassis,etc these are  all bad choices instead go directly to the chassis .good luck.