But remember that link leads to a post that is 5 years old.
I recommend using 6 (six) AWG wire to feet that pretty, dual contact plug and socket. The wire is going to be exposed because it passes under the truck. Use a GARDEN HOSE or heater hose to act as a protective cover and keep it well away from the exhaust system.
You are going to need CIRCUIT BREAKERS at BOTH ENDS.
Under the hood
At the Camper batteries
Two breakers
FORGIVE THE IMAGE EXAMPLE Choose 120-amp breakers
http://www.delcity.net/store/Hi!Amp-Surface-Mount-!-%3Cbr%3EManual-Reset-%28Switchable%29/p_193073An auto body shop has the tools and expertise to cut a good looking hole in the truck fender.
Since your battery is AGM you can mount the breaker right next to the RV battery. The best place to take power -from- the truck is right at the alternator output stud. The big one. Mount the truck-side circuit breaker on a fender well.
You're not going to believe how much faster and more correct the improved system is going to charge the camper batteries. The parts I listed are fine for one or (2) AGM batteries.
The system components I chose are automatic except for the breakers which must be reset manually if shorted. The battery isolator is TOTALLY AUTOMATIC. No switches, no wires. It's the proven hot setup...
