The process is:
Cut eggcrate panels to apply foam to
place anything you want in the foam on the eggcrate and then foam around it (I'm using some dried rock for tunnels and Great Stuff foam
Cover foam in epoxy and spinkle with sand and crushed coral for more natural look and to protect the foam from UV (I'm using Epoxy)
here some my pictures :
Cut eggcrate panels to apply foam to
place anything you want in the foam on the eggcrate and then foam around it (I'm using some dried rock for tunnels and Great Stuff foam
Cover foam in epoxy and spinkle with sand and crushed coral for more natural look and to protect the foam from UV (I'm using Epoxy)
here some my pictures :