Hi Lufria, I'm mounting a sprung chassis on the one90 for a teammate, and already mounted a hummer chassis on my rbk 7k. I would say that it is really hard to mount the hummer chassis under a one90, there is already a "hole" in the outsole, if it fit you are really lucky. But if it not fit, you have to dremmel out a bit and that would be really hard on the one 90.