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What kind of devices are you planning on powering? You are probably better off running a dedicated circuit as opposed to tapping into an existing circuit. For exterior mounting you will want a weatherproof or marine grade receptacle. How and where you mount it is up to you. Do you want it stealth? In your bumper? etc
...what's the "proper" or say typical amperage for a 12v socket? 20, 30, 55 AMP? Or do the higher-power devices have different plugs? 10ga wire is big and harder to place in the cab, so maybe I could go with 12ga and a 20A breaker inside, and up to around 60A for the bed. I will need another battery of course (deep-cycle) and a heavier alternator.
There have been plenty of times I could have used a quiet modest capacity generator.
A 6 place fuse box would give you a place to power a few sockets per fuse. Run some 4 gage wire with a circuit breaker in line to it.