1 - Yes it's always hot..... You could put in a relay that's triggered by a wire from the center console which is only hot in Accy or Run. A little more complicated but very doable.
2 - The power rear hatch has to be initialized, accomplished by manually pushing the door shut. The radio will need the passcode you put in at the dealers....... that's all I've ever had to reset.
3 - I'd start with a 20 amp and see if that will work, then a 30 amp etc...... The wires on the 12v outlet are long, cut to length. I actually replaced them with 14g as I don't really trust chiniziam wire (probably 18g if that). 12v outlet is labeled + and -
A really cheap and easy place to obtain piece of metal.... are commercial wire junction box cover sold at Home Depot/Lowes/Ace. They are easily bent with a vice and a 2x4 and a hammer. Place the metal in a vice at the depth of the bend, start you bend with your hands to 20-30 degrees then use the 2x4 (or similar) as a wide punch. Rest/place the 2x4 on the vice jaws and strike it with a hammer. This method distributes the force across the with of the metal and you'll end up with a tight radius bend vs a rounded bend that looks like crud.
You might think about changing the plug on the fridge to something below. and with a battery tender lead, the fuse holder and ring terminals are already installed and with the 12v outlet plug you retain the versatility but the tender 2 pin connector will not shake out etc.... .
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