Trailer wire question

[sschevel]

Well, after a few hours searching the net, I am confused, I hope you can help with what I need.
I have just purchased a 98 Explorer.
I have also rented a popup camper that is wired with a 7 barrel plug.
I am looking to find the wiring that I need to connect to that trailer.
I see a $50 kit that draws power from the battery and connects to the wiring in the rear lights, but its output is a flat 4 plug. Then I see a 7 barrel plug for another $20. The local uhaul stated that they would put in the barrel plug for around $80.
I am not sure what "kit" they use, or how much of the 7 wires they use on the barrel plug.
I was told that I could use a flat 4 pin to barrel adaptor, so I know the trailer does not use all 7.
I just feel that if I am spending the money, I should get the barrel plug, that way I am ready for any "future" trailer pulling.
I also would prefer to do the work myself for both the knowledge of, and the satisfaction of doing it.
Part of the problem is that I dont understand what all the 7 barrel does, and I doubt that the $80 quote from Uhaul includes wiring all 7 ______.
I plan on getting the Class III hitch, and I have seen a Hidden Hitch for $125. Again, the quote from Uhaul is like $180, which is WAY to much, and I can bolt an item on just like they can.

For now, I plan on using the bumper atleast for the first weekend in May camping trip, and I will have to get a better hitch later in May.
Thanks for your time, and help
Guy

 

[Crankcase]

A 7 barrel plug has the following connections:

4 prong connector:
1 Ground
2 Tailights
3 Left turn
4 Right turn
----------------Plus:
5 Reverse lamps
6 Electric brakes
7 Live wire

If you plan on getting a big trailer, get the 7 pole connection in your truck. But if you are going to pull a boat or something light, just get one of the 4 pole connections that plugs into the factory harness.