Greetings Rick F!
I am most familiar with the first generation (1972-1979) Argosy travel trailers so will answer from that perspective.
- The fresh water tank on all of the standard coaches was mounted on top of the floor with most being mounted immediately below the front panoramic windows. There is any particular attempt at additional insulation, and any heat that reaches the area inside of the cabinet is radiant/convection as there isn't a duct to that area in most of the coaches.
- The blackwater tank is also mounted above the floor immediately under the toilet. Again, there wasn't a particular effort to insulate the tank, but on most of the coaches there is a furnace duct that supplies heat to the area.
- The gray water tank on the Argosy trailers can be either below floor (standard series coaches) or above floor (Minuet coaches). If my information is correct, the gray water tank became an option in 1973 and was made standard in 1974. There is a small duct opening serving the below floor bay where the gray water tank is located as well as some insulation around the tank. On the Minuets, the gray water tank is above floor and does not serve the shower drain. The Minuet's gray water tank does receive some heat flow from the duct that serves the blackwater tank area, but the flow is very minimal.
As with everything Airstream, there is little absolute . . . . and when previous owners' attempts at upgrades and changes are added to the puzzle the answers become even less clear.
I have found my Airstream and Argosy to be every bit as cold weather capable as my prior Nomad, but there are other manufacturers who make coaches with more comprehensive cold weather packages.
Good luck with your search!