It would be very simple to plug a compressor into a plug at the back of the vehicle, but for me it is a better option to use the spare space under the bonnet. I agree with David, if I get mud and water into the battery box, I have WAY bigger issues than a drowned compressor. Access to the outlet and switch is super simple and removing the compressor is very easy if required. A couple of pix attached. (my first try at attaching pix, so I hope it works)

