I have built five or six Bandits over the years, and have found that a great place for the retract and brake air tanks is behind frame F-6. Secure the tanks to the fuselage floor with a small strip of silicone sealer, barbed fitting forward through the rectangular opening at the bottom of F-6.

Nothing else will be mounted in that bay anyway, and the heat from the tailpipe is not a factor.

Here's a couple of images of the installation. Sorry for the poor quality of the pix, but I'm not much of a photographer, and the area is hard to see and illuminate with the bypass and pipe installed.
You can see a much better picture of the area on page 28 of the Super Composite Bandit manual.