Is their anyway to hook up a couple of turntables so that I can play them out of my trunk? I was thinking that I could hook up the mixer stright to a 4ch amp. This would allow me to power my subs as well as my 4 way 6x9's. Would this work, or am I missing something?

should work just fine.
just use a high end inverter that puts out a pure sine wave to power the tables and mixer

Where exactly do I connect it to?

wire the inverter into your cars wiring system then just be able to plug in the tables and the mixer after that you will need some sort of a y adapter to y out to the 4 channel amp. as far as the amp goes i don't have a clue how you would wire the remote line. if your cd player has input you might be able to input the tables and mixer into that and then use it for going to the speakers. and amps'