When I made my strip/string diamond quilt, I didn't have the strip tube ruler and I just used my square ruler instead. I got the idea of how to do this from the MSQC video here:
https://www.youtube.com/watch?v=vOWSp0mTTqE
I didn't find it too difficult at all. FYI - I wasn't making squares. I just made triangles out of three strips to start and then built my diamonds from that. Not sure if that will make a difference for you as I haven't actually looked at the pattern you're making.