Good luck with the swap! Btw, I have Siporax in my overflow as well, except I used a 20lb fishing line and threaded 4 lines the height of the box and connected them up top and bottom, was able to fit their entire box full that way with minimal footprint.
A couple people mentioned in my video the fishing line trick. I NEVER thought about that. So you have any picture of the top? How is that working out for you?