'73 sovereign floor metal

[Flaboy67]

Does anyone know where I can purchase the 5" channel for the floor supports in Florida?

[DanielB]

I assume that you are asking about the C channel that is the chassis.
The pieces that go crosswise are generally called cross members.

That particular thickness of those C channels is really thin and plus they have the big holes cut all in them. That will be pretty hard to find.

A tip that I got was.. the most generally available 5" C channels are at 6.7 lbs per foot and 9 lbs per foot and are available at steel distributors. Those you can get.

I used the 6.7 lbs per foot (C5x6.7) for a new frame, but don't know how appropriate they would be for mix and match with an existing frame.
What worked for me, and I live near Charleston, SC was..
Google, "Steel Charleston" and called some steel distributors. It is not very expensive and the one that I talked to would even cut it for me if I wanted.

[wasagachris]

Flaboy crossmembers are available from any Airstream dealer. Most will have to order them. Here are two that usually stock them.
Inland RV Center Inc.

Frame Cross Member 410766 [410766] - $79.95 : Out-of-Doors Mart!, More Airstream Parts on-line than anyone!

Inland RV has a better price than Out OF Doors Mart. Inland is in California and OODM is in North Carolina.
Both also sell the outriggers which go on the outside of the frame rails to support the outer edge of the shell.