I just used what I had at hand right now. I found some large galvanized finish nails that I bought a whole case of along time ago. I stuck about 12 or fourteen in the floor recess. I was going to hot glue them in but they are trapped tightly. That added the 3 ounces I needed. I'll have to see if that's enough.
I need to order more stick on weights for the future. Money's tight right now.
I had just 2 SUVs in one car from the old dollar store stock. They weighed more than I could probably fit in the floor. Maybe I will look at more of them down the road too. I think they'll be too heavy for the top though. So the silhouette idea might be better up there?