If you'r worried about the integrity of the foam, you could always reinforce it from the inside. If you hot glue strips of cloth over the seams, even whole sections, you'll be able to add more weight w/o compromising integrity.You could cut out the areas that you would need to get in to like the battery pack and your creeper-cam........I mean your GoPro :facepalm
Ahem - i prefer to call it my HoePro as it is clearly just for recording fema- ok just kidding. I'll look into this! Thanks for the tip