First thing as far as solar is to determine your needs. How many watts how many hours a day? Insulation is pretty much determined by the outside temps and how much of a heat source you will have verses how much space you are willing to loose to insulating...
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a)
First thing, I think -- eliminate a bunch of First Worlder stuff.
Evaluate your need for:
* dual wine-chillers and electric fireplace in the 'entertainment center'
* hair-dryer
* earthquake-car loudspeakers
* second galley and 'entertainment center' with big-screen on the patio
* can you somehow struggle along without a 14,647cf side-by-side fridge-freezer with room for decades of left-overs?
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I think insulation ought to be excessively obsessive.
We start with:
* adhesive-back acoustic against the outside wall, a gap, then
* one-inch pink-board, another air-gap, then
* two-inch foil-side poly.
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A peripheral aspect of insulation is windows.
In our ExpeditionVehicle, we mounted 3010 (three feet wide by a foot tall) dual-pane sliders designed for a stand-still house.
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Our cab is separate from our quarters, so those yuge single-pane windows up-front are less of a concern.
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We rarely operate our heater -- one Wave 3 catalytic heater set on 'LOW' -- above about 40°f.
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Reduce humidity and fungus with open windows on opposite walls.
For us, this's a quarter-inch on one side, a half-inch on the other.
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Are you over-wintering in Alaska?
If I was me, I might have a Plan B, Plan C, and maps for Baja beaches.
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b)
Although certainly adequate as a shelter, your 1500 offers a very limited GVWR.
I can easily see a ton of canned goods, water, tools, batteries, propane, cook-gear.
And security... for the frontier.
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Riding -- or exceeding -- the GVWR is one of my nightmares.
For your next rig, we think you could avoid it by choosing a stouter commercial truck with excessively obsessive cargo capacity.
And a place to walk upright on your hind legs.