Auxiliary electrical power for car

[LargeMarge]

...i was told to change oil at 3000 miles instead of 5000
someone suggested a temp gauge. maybe with a warning when water reaches a certain temp .

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a)
Driving an engine is a different can of worms compared to extended idling.
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Example:
In the olden days, during federal-mandatory off-duty hours, a semi driver might idle the rig to keep the cab comfortable during rough weather.
The problem:
* an idling engine allows unburnt fuel to slip past the piston rings.
That unburnt fuel eventually drains into the crankcase (aka 'the dips').
As you might suspect, fuel makes a poor lubricant.
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So...
Two things happen simultaneously:
* excess fuel worshes the lube from the cylinder walls, drastically reducing time-between-overhauls (TBO)
* fuel in the lube dilutes its ability to lubricate, plus reduces its ability to transfer heat from critical components.
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I think your idling plan has merit... in some circumstances.
I think a different plan could save repairs.
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Of course, none of this is applicable in California.
As I understand it, idling is limited to four (4) minutes.
Real-World:
My sister over-nighted near frisco.
Next morn, she started the rig to build air while accomplishing her federal-mandatory walk-around.
Apparently, she exceeded the four-minute rule, and received an expensive ticket for her efforts.
Who snitched?
The mail-delivery gal... idling nearby while fussing with the post... federally exempt from state rules.
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California, federals.
Do not get me started.
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b)
I think we can all agree, we can spot a live-aboard pretty darn easy.
Accordingly, the concept of 'stealth' is kaput.
Let's retire 'stealth', it does not exist, it never existed.

 

[BlueMarkOhio]

Ideal is to get a plug-in hybrid that has "camper mode", like a Prius, Sienna, or Pacifica (with an easy mod).

But if you are staying with an ICE vehicle, you can install an upgraded alternator (or a second one) to connect to a power bank (Jackery et al), that will be kept charged when driving. In extremis you can charge it by idling. No need for solar panels, but that would always be an option for later.

The most economical way to heat would probably be a diesel heater ("Chinese" heater), but that is not ideal if you want to avoid fuel. Electric heat would require very high capacity, as would A/C.