If the trailer doesn't have a battery, how does anything in it work (lights, water pump, etc.) once you are set up and camped? Hookups to an electrical panel?
For 12V power on the road, you'll need the same 6-conductor plug on your tow vehicle with the additional power conductor wired in to your hot/alternator/battery, or an auxilary battery; a simple 4-6 adapter won't do you any good, as only 4 of those 6 will be operational, although I suppose you could also run a single additional wire from your tow vehicle to the trailer.