Black and Grey Tanks on a 61

[DWH]

I am restoring a 61 22' Spaceliner. The only holding tank it had on it was the fiberglass one under the toilet. I am adding a couple tanks and unclear on the best way to secure them in. They are the ABS style tanks and sit perfectly between the frame rails. Any pictures or idea would be awesome! This picture is an early one when I was mocking it up to show location. I am just not sure how these things are held in from the bottom. Are the securely attached or is there a little play for expansion?

[putback]

Certainly not THE answer, but some results. I've stuck with the origianal Airstream method. Galvanized sheet metal pan to support the tank, lined with insulation, chocked with pressure treated shims, with no problems. A friend tried a direct attach similar to your picture and his tank cracked where it contacted the frame. He did use quality 1/4" rubber strips to cushion the contact area. Just one instance, but.