This is meant to be a new thread, but apparently I don't have permission. It does apply to this thread, though. It's about the spray-on insulation under the trailer.
Last week, we were returning from a stay down on the North Shore of Lake Mead in our 17A. Our path brought us into Bend, OR, from the west on US 20. We decided to stay the night near Prineville, and woke to a surprise. Everything was frozen! It had gotten down to about 10 degrees F overnight. I leaned down to look at the fresh water tank: frozen. Fortunately, not full, so there was room for expansion. Luckily, things thawed out the next day, and it appears that we dodged the bullet.
When we were going through the build sheet, we never dreamed that we might need the insulation, because we didn't plan to camp in the winter. I wrote a note to ETI, asking about a 12 heating strip to be applied to the tank. ETI wrote back: "Yes, available, but part of the under-insulation package. Cost about CDN1200, can be done after delivery."
So here's my two cents: get the under insulation even if you think you won't need it. You might be surprised!