From what I observed on my trucks is that trailer wire is usually 10 ga, what theoretically is good for about 40 amp, but on other side, when you follow the wire from the alternator via truck bumper plug, back to camper cord and then to camper battery - you will find 30 to 40 ft of wiring, what will create quite a resistance and with resulting voltage drop, the charging current will be greatly reduced.
I consider that a good thing as charging 100 am-h battery with 40 amp can overheat it and will shorten its life.
Meaning in natural way you will get you battery charged maybe in longer period, but without much danger.
This has been working in RV for well over 50 years, so why change it?
