UPDATE
So, I am getting ready to slice into the foam -- I was all set to create a velcro hinge for my foam flap, to drill into the cabinets for vent holes, yada yada yada -- and I decide (for reasons of diplomacy and domestic tranquility) to check with DW. I drag her outside to the trailer to explain the whole thing.
She nods and says (politely), "Good idea! But how is this so different from a hot water bottle? I could boil water on the stove, fill the bottle, and put it on my lap, under my lap blanket, while we are eating dinner or reading." (That's how cold it gets when we boondock -- we often use lap blankets and wear warm ski hats while we are inside.)
I sputtered a little, disappointed that I was not going to get to do yet another "mod." But she had a point -- yes, it is a little more trouble to boil the water and fill the bottle. And it might waste a couple of quarts of water per night. But it means that the water heater will not have to cycle on and off, I don't have to cut the insulation, I don't have to drill any holes, and the heat is right where she wants it -- under the blanket -- rather than indirectly warming the interior of the trailer.
Darn.
