'71 Starcraft Wanderstar- "The Hilton"

Thoroughly enjoyed this post. I feel like a child by even suggesting something after reading your wealth of knowledge and experience, but I do have a suggestion about your tank heating issue. You mentioned using the heated gutter cables, which as you said may be overkill except for extreme cold. What if you used the heated cables as the primary heat source, but also supplemented that with standard heated pipe tape? The stuff you see on water spigots and home plumbing. Wrap it around the exit/valve and back under the tank. Use it for moderate conditions but have the ability to "turn on the heat" of the gutter cables during extreme cold.
The heat tape alone probably wouldn't keep a full tank from freezing, but it should work around the valve/exit area and pipe.