Hi M. Tate,
Sorry I haven't followed the thread, just tune in infrequently when a
computer is available.
To be sure, there is a foam surround inside the sheet metal housing for the
black water tank. The foam that contacts the tank consists of a series of
pylons about 3 inches in diameter. The follow the contour of the bottom of
the tank to provide support and maintain the proper drainage. The pylons
are to allow warm air from the furnace to flow around the tank and prevent
it from freezing. Same as other areas behind bulkheads for the bathroom
plumbing, and the potable water tank (pump), etc. This is the reason I used
the original foam and filled in with urethane foam from Lowe's, NOT LATEX.
You could use the blue home insulation. And on a flat piece, glue circles
such that the top of the tank would be covered with a sheet of the same blue
insulation, yet level with the top of the sheet metal housing. The tank
must be held up so as there isn't any tension on the toilet fastener thought
the floor. If this hangs, it will shortly break out the top of the tank.
My opinion that it's important that the unit be forced up against the floor
to keep it from bouncing inside the housing.
You may use polyurethane foam and just fill under and over the tank if you
can keep the drainage level proper and maintain about 1 inch foam around all
the sides and top of the tank. Sort of defeats the purpose of the Airstream
engineered heating of the holding tank. Messy when it freezes during a long
cold day/night and you can't get the ice to thaw enough to dump the filled
tank! Personally, the blue foam seems better as it's hard enough to stay in
place, can be glued, and should have a long life as it's used for home
insulation. Think the stuff is polypropylene or something like that. Other
than this, I'd sure get a unit with both black water and gray water tank as
an original accessory.
I'm not sure what the felled tree had to do with the tank housing problem,
but . . . If the housing was rusted out, the holding brackets, if it has
them (some models in the early 60 screwed the sheet metal directly to the
floor). Newer models have a cross support of angle iron to support the tank
housing and thus the tank. Keep in mind that the toilet hold down screws
out of the holding tank - counter clockwise to loosen and it can be very
tight. I welded a tool to remove the hold down, but used a not OEM hold
down for the replacement.
Don't know if this helps, but . . . the advice/information is free and
mostly that is about what it's worth.
Regards, '69
Safari, Joy