I can't promise you that you will be able to connect to silicone pipes together with that little space. You will need very small pieces of 3" tube that you can band clamp. Even then, because the pipe squeezes through and loses its shape, it will be hard.

I don't know anyone who has actually done this, so i don't know that anyone can actually speak from experience. It might be easier if you use a metal 3' 90 degree bend instead of silicone.