Need some ideas/help with this bear canister setup

I need a way to carry my bear canister on the back of my bike. I currently am having troubles cause I also need my tent to go back there too. This is the best setup I’ve found so far but there is still too much play.

Any ideas on what I can do to really secure the bear box on the back with my tent? These straps are 40inches and are completely maxed out with this setup but it’s still not sufficient enough for touring on gravel.

Any and all ideas are appreciated!

Thanks!