I went to a commercial car store showed them the compressor and the details and then used the correct rated wire. Ran that straight off the battery as would not advise running through the car electrics. ALWAYS check what your doing with someone qualified - it is a tricky thing - don't damage the car or the electrics or the compressor and be mindful of heat.
BUT the best way would be to use a good carbon bottle - get a small home compressor, then its way way quicker to fill from the boot, the bottle is not heavy so can be easily moved, plus with a home setup its far easier to manage and quicker. Will cost few more pennies but way way simpler.
Over all, before you do anything clever with the wires get advise and get it checked for safety.