Check with your state DMV to see if you can raise your GVW if you would like it to be higher than 16,000. Some states allow you to go higher, but it also usually cost more to do so. Other states out there won't let you raise it at all, unless you put a tag axle, for example, on it. In my opinion if your factory GVW is at 16,000, the truck should not be carrying anything near 24,000. If your state allows it, I personally would not go any higher than 18,000, for safety reasons. Once you establish your allowed GVW, you can then get a quote from your insurance company.
Bill