I see your point and hope it works for you. I just question running that switch right at it's limits. They have relays that could go too. Hopefully a fuse burns out first. I'm not enough of an electrician to know if a 40amp compressor can heat up and go beyond it's rating? Think I would find that out when living on the edge of rated amperage. Only trying to help cause if this works I might do the same. I have 10ga going to my little panel in the bed, but would have to rewire the panel like you.That's the most conventional plan for sure. The main point of this project was to power my compressor at the rear of the vehicle. This allows me to store & use my compressor and hose octopus right from the bed. I did run the engine during my test ... as that's how I will do it at trail heads as well. I also already found the wire at a reasonable cost, ran it, and connected it.
I connected to Aux 1 (40amp) so that I could control when the bed was receiving power. I'm pushing the limit of that 40amp fuse, but I'd be annoyed having to wire my own switch when I already paid for the aux switches. The compressor seemed to draw between 30-40amps. I blew an in-line 30amp fuse on my first trial before replacing it with a 40amp fuse. It was on the 2nd trial that the fuses held up ... but the 4inches of thin 18AWG wire between my 6AWG wire and the cig outlet decided to become kindling.
I could re-think the whole set-up, but I'm not yet willing to accept that. I'm hoping that the cig outlets can handle up to 40amps. (All of the conductive connections in the component seem to have cross-sections greater than or equal to a 10AWG wire.)