What EXACTLY are you doing? Not a summary, not a type of thing, but exactly what are you powering, including pictures and/or links?
There is no need to go through any of this just to produce heat. A mere resistor connected to 12V will do that more efficiently at the single point where it's needed unless it's an ignition source and you need maximum heat density.
This is another one of those topics that becomes a large time-sink because all specifics and requirements were not laid out concisely at the start. Now you're talking about robots, then switches, and still not linking to specific things, lol.